WO2013160749A2

WO2013160749A2 - Hydrophilic polymer surface, process for production of the same, uses of the process and items comprising said surface

Info

Publication number: WO2013160749A2
Application number: PCT/IB2013/000766
Authority: WO
Inventors: Mirko MAZZURANA; Ruben BARTALI; BENSAADA Nadhira LAIDANI; Francesco MOZZI; Gloria GOTTARDI
Original assignee: Fondazione Bruno Kessler
Current assignee: Fondazione Bruno Kessler
Priority date: 2012-04-27
Filing date: 2013-04-26
Publication date: 2013-10-31
Anticipated expiration: 2014-10-27
Also published as: ITVI20120101A1; WO2013160749A3

Description

HYDROPHILIC POLYMER SURFACE, PROCESS FOR PRODUCTION OF THE SAME, USES OF THE PROCESS AND ITEMS COMPRISING SAID SURFACE.

DESCRIPTION

Technical field of the invention

The present invention concerns a hydrophilic polymer surface, preferably having a contact angle smaller than 20°. It also concerns a process for the production of such a surface, a use of the process and items comprising said hydrophilic polymer surface.

State of the art

Many accidents at work and road accidents are caused by scarce visibility, especially when the environmental conditions are unfavourable. Scarce visibility is due to the fogging of viewing aids or to the formation of drops on the same. Hydrophilic surfaces are very promising in the sector of personal protection equipment or of optical elements in general to ensure good visibility. In these sectors polymers are extensively used thanks to their excellent optical properties and to their mechanical resistance. Unfortunately, polymers have low surface energy and consequently scarcely hydrophilic surfaces that favour the formation of drops on the surface of the polymer in environnients where relative humidity is high or in the presence of rain. The drops that form in those situations cause two types of phenomena:

a) light scattering due to the lens effect induced by the drop itself and b) surface fogging.

Both phenomena reduce the degree of safety of the devices made with polymeric materials, thus reducing the clearness of images and therefore the actual perception of the field of view. It is thus absolutely important to modify the solid-liquid interaction of the surface in order to increase the hydrophilicity of the same. If the liquid is water, the interaction is called wettability and can be studied through measurements of the contact angle.

Hydrophilia, often called also hydrophilicity, is generally understood as the physical property owing to which materials or individual chemical species (for example molecules) tend to bond with water. Below in this description, a surface is considered hydrophilic (hydrophile) when it has a contact angle included between 0° and 90°. A surface is considered superhydrophilic (superhydrophile) when the contact angle is smaller than 5°. A definition of the term "superhydrophilic" can be found, for example, in Yosuke Tsuge, Jinho Kim, Yuji Sone, Oriha Kuwaki, Seimei Shiratori, Thin Solid Films 516 (2008) 2463-2468. In this case the contact angle obviously refers to a liquid that is water.

The wettability of a material can be modified with different methods, including mechanical and chemical methods. A technique that is applied to intervene on the wettability of surfaces is the plasma technique, which is capable of modifying the external surface of a material in a controlled manner in nanometric scale and thus changes the solid-liquid interaction of the material treated in this way without affecting the inherent qualities of the material itself. J. Lai et al. (in: "Study on hydrophilicity of polymer surfaces improved by plasma treatment, Applied Surface Science 252 (2006) 3375-3379) modified polycarbonate, polypropylene and polyethylene terephthalate with an argon plasma, obtaining hydrophilic surfaces with anti-fogging properties. They ascribe this positive effect mainly to the formation of groups C=O.

D.Y. Chen et al. (in: "Photocatalytic Ti0₂ thin films deposited on flexible substrates by radio frequency (RF) reactive magnetron sputtering", Current Applied Physics 12 (2012) 179-183) deposited titanium oxide on polycarbonate with an argon plasma, obtaining high hydrophilicity of the surface covered in this way after irradiation with UV rays. Other papers propose that the hydrophilicity of polymer surfaces be modified by applying tensioactive agents (for example, L. Irusta et al. in: "Migration of Antifog Additives in Agricultural Films of Low-Density Polyethylene and Ethylene-Vinyl Acetate Copolymers"; J. Appl. Polym. Sci., 111 , 2299-2307 (2009)) or by treating the polymer surface with chemical agents (B. Mohammadhosseini in: "Povidone-iodine surgical scrub solution prevents fogging of the scop's lens during laparoscopic surgery", Surg. Endosc. (2010) 24, 1498-1499; Amy R. Brackeen et al. in "Surgical Pearl: Antifog solution for surgery goggles", J. Am. Acad. Dermatol., October 2006, 694-695).

M. Nie et al. (in: "Superhydrophilic Anti-Fog Polyester Film by Oxygen Plasma Treatment' - Proceeding of the Nano/Micro Engineered and Molecular Systems, January 2009, Shenzen, China. NEMS 2009. 4th IEEE International Conference; p 1017) describe how the treatment of a polyester film with an oxygen plasma results in a surface with superhydrophilic anti-fogging properties, on which a water film is formed instead of water drops. This superhydrophilic characteristic of the surface is ascribed to the presence of COOH and COH groups generated by the plasma. Also P. Patel et al. (in: "Superhydrophilic Surfaces for Antifogging and Antifouling Microfluidioc Devices"; JALA, April 2010, p. 114-119) obtain anti-fogging properties for a polyester film by using an oxygen plasma treatment and introducing polar groups in the surface. The surfaces treated in this way maintain optical clearness also in the presence of high humidity, since water forms a film instead of drops on the surface. Wettability is a process strictly related to chemistry and morphology in nanometric scale of a surface. The increase in wettability (hydrophilicity) determines the flattening of the drop on the surface. The decrease in wettability, instead, leads to a tendency of the drop to assume a shape that is increasingly similar to that of a sphere, thus minimising contact with the surface.

The plasma technique modifies the most external layers of the material in a controlled manner. The modification caused by plasma consequently changes the solid-liquid interaction.

In the state of the art, documents are known which describe polymers treated with argon plasma, and not air plasma, and comprising gold, for which in some cases hydrophilic properties are not reported, or whose polymer/water contact angles do not reach values that can be ascribed to superhydrophilicity. Alena Reznickova et al., for example, in "Nano-structuring of PTFE surface by plasma treatment, etching, and sputtering with gold' (J. Nanopart. Res. (2011) 3:2929-2938) explain that plasma ablation of the polymer with the consequent reduction of the contact angle serves to prepare the polymeric surface for the successive deposit of a continuous golden layer. The presence of gold is not considered responsible for any particular effect on the contact angle. Jakub Siegel et al., in "Annealing of gold nanostructures sputtered on polytetrafluoroethylene" (Nanoscale research Letters 2011 , 6: 588) describe gold nano-layers on polytetrafluoroethylene (PTFE) but do not give any indication regarding the effects of gold on the contact angle. Yu-shan Chen et al. (in: "Electrochemical impedimetric biosensor based on a nanostructured polycarbonate substrate"; International Journal of Nanomedicine 2012:7 p. 133-140) use RF magnetron sputtering under argon to deposit a gold film on polycarbonate and thus obtain an electrode/biosensor; hydrophilic properties of the polymeric surface coated in this way are not mentioned. The values of the contact angles achievable for polymeric surfaces (not smaller than 44° for polystyrene, polyethylene terephthalate, polyethylene and polymethyl methacrylate) coated with gold through plasma sputter as described by Gilson Khang et al. (in: "Platelet and cell interactions on gold sputter-deposited polymeric surfaces"; Bio-Medical Materials and Engineering 8 (1998) 299-309) are not promising for the use of the described treatment in order to give superhydrophilic characteristics to polymeric surfaces or in any case to obtain polymer/water contact angles < 20°.

Presentation of the invention

Considering the promising properties of superhydrophilic polymer surfaces and the possibilities that plasma treatments seem to offer, it is the object of the present invention to propose hydrophilic polymer surfaces with optimized anti-fogging properties as an alternative to the already existing polymers with superhydrophilic surfaces. Special importance is given to the object of providing hydrophilic polymer surfaces (and a process for production of the same) that also have anti-light scattering properties, especially in the field of optical elements. Up to now the state of the art has dealt mainly with anti-fogging characteristics and neglected the studies on anti-light scattering properties.

The objects described above and others that will be highlighted in greater detail below are achieved by a polymer as defined in the first claim, and in particular by a polymer of the type mentioned at the beginning, in which the hydrophilic surface comprises gold. Preferably, the contact angle with water is smaller than 20°, even more preferably < 5°. None of the documents mentioned above concerning surfaces comprising gold describes polymer/water contact angles < 20° or even < 5°. Preferably, the contact angle is determined with a drop of water approximately 2 μΙ in volume resting on said surface. The water used is preferably milli-Q water (purified and deionized with resistivity of 18.2 ΜΩχαη).

A small contact angle of the water drop on a surface is a parameter that indicates high hydrophilicity. Contact angles smaller than 5° mean superhydrophilicity. The anti-fogging safety glasses available on the market have a contact angle that exceeds 20°.

The presence of gold on the surface regards the most external layers, preferably the nanometric layers of the polymer. The polymer surface is advantageously the surface of a shaped polymeric body.

Surprisingly, the inventors have discovered that the presence of gold on the surface of a polymer induces anti-fogging properties and also anti-light scattering properties in the polymer without affecting the optical characteristics of the polymer, as has been shown by transmittance and reflectance measurements. These two properties result from the high wettability of the surface, which avoids the formation of drops and favours the formation of a water film. In fact, the polymeric surface according to the invention remains transparent to visible light, which does not seem verisimilar for surfaces with continuous golden layers as described in some documents of the state of the art.

A wettability index for a surface is the contact angle. The contact angle is a thermodynamic quantity defined by the angle formed by the contact between a liquid-vapour interface with a liquid-solid interface or, less typically, a liquid- liquid interface. For an ideal surface, meaning a smooth and homogeneous surface, said quantity is defined by Young's relation:

Ylv C0S9 = Ysv - Ysl,

where γ_5ν is the solid-vapour interface tension, γ₅ι is the solid-liquid interface tension and γι_ν is the liquid-vapour interface tension; in the cross section of a liquid drop deposited on a solid, the contact angle is the angle included between the direction of the solid-liquid tension and the direction of the liquid- vapour tension, tangential to the external surface of the drop, with vertex in the three-phase liquid-solid-vapour point. According to these hypotheses, the contact angle corresponds to the thermodynamic quantity that minimizes the free surface energy of the system.

According to a preferred variant embodiment of the invention, gold is present at least partially in the form of gold oxide. Gold oxide is advantageously AU2O3. Extremely low values for the contact angle were observed when the atomic percentage of gold in the form of oxide exceeded 10% as determined through XPS (X-ray photoelectric spectroscopy) analysis. In preferred variant embodiments of the invention gold is present both in the metallic form and in the form of gold oxide. The total atomic percentage of gold determined through XPS is preferably approximately 30%.

In the documents described in the state of the art, in the presence of gold there are no clear indications regarding the presence of gold oxide, in fact the plasma treatments with gold deposit take place under argon and not in the presence of air. D. Briggs and M . Seah, in "Practical Surface Analysis", vol. 1 , second edition, John Wiley & Sons, New York (USA), 1993, indicate as bond energy for metallic gold 83.99 eV (Au4f7/2) and 87.66 eV (Au4f5/2) and for gold in Au₂0₃ 85.78 eV (4f7/2) and 89.46 eV (4f5/2).

In a preferred variant embodiment of the invention, the hydrophilic surface has been obtained through a plasma treatment in combination with a cathode spray with a gold target. Advantageously, the surface is superhydrophilic.

Plasma makes it possible to modify the surface portion of a material without modifying its intrinsic characteristics. When plasma interacts with matter the result is mainly the modification of the treated material: reactions take place between the surface and the gaseous species which lead to the formation of functional groups and cross-linking among chains in the case of polymers. The invention, however, has unexpectedly revealed that the combination of the simple plasma treatment with the application of gold on the treated surface results in a considerably reduced contact angle with the consequent achievement of anti-fogging and anti-light scattering properties. This application of gold is performed by means of a cathode spray (sputtering). Sputtering is a process whereby atoms, ions or fragments of molecules are ejected from a solid material (target) hit by ions. This phenomenon takes place as charged ions hit the surface of a cathode (target) that owing to a ballistic effect releases atoms that are sprayed on a substrate. The impacts with the ions that bomb the cathode surface can penetrate it to a depth of 3-4 atomic layers.

To advantage, the polymer is polycarbonate. Even other polymers can be considered, for example polyethylene, polypropylene, polyesters etc. Polycarbonate is a widely used material in the field of accident prevention and safety at work, for example for the production of safety lenses, optical lenses, visors, protective barriers. In these applications anti-fogging and anti-light scattering effect is particularly important. The wide use of this polymer is due to its unique characteristics of transparency in the visible spectrum, resistance to impacts and lightness.

A second important aspect of the invention concerns a process for the production of a hydrophilic polymer surface, preferably with a contact angle smaller than 20°, comprising the following steps: a) preparation of a polymer surface;

b) preferably cleaning of the polymer surface;

c) treatment of said preferably cleaned surface with a plasma treatment in combination with a cathode spray with a gold target.

Advantageously, cleaning the surface before treatment avoids undesired reactions of plasma with the foreign materials present on the surface.

Even for this process, the preferred polymer, especially for optical and/or safety applications, is polycarbonate.

According to a preferred variant embodiment of the invention, the plasma is a cold plasma. Polymers tend to soften, melt or decompose at high temperatures, therefore a low temperature treatment is gentler. Plasmas that are generally considered cold plasmas are described, for example, by A. Grill in "Cold Plasma in material fabrication", 1994, Wiley, IEEE press.

Advantageously, the gas used in the plasma treatment contains oxygen, which favours the formation of gold oxide. Preferably, the gas is air.

In a very preferred embodiment of the invention, the plasma treatment with cathode spray is performed at pressures included between 0.06 and 0.1 Torr, preferably at 0.08 Torr. Experiments have shown that at these pressures it is possible to obtain contact angles smaller than 20°, preferably smaller than 15°. In the case of a pressure of 0.08 Torr, a contact angle < 5° is obtained. XPS studies have shown that an increase in the gold oxide (AU2O3) concentration on the surface results in a smaller contact angle. Furthermore, the sample obtained with a pressure of 0.08 Torr features optimal transmittance of at least 75% in the visible.

Preferably, the plasma treatment with cathode spray is performed during time intervals included between 30 and 180 seconds, preferably time intervals included between 120 and 150 seconds. These times represent a good compromise between a sufficiently effective exposure to plasma and an exposure that modifies the polymer only superficially.

Another aspect of the invention concerns the use of the process according to the invention to give optical elements anti-fogging and anti-light scattering characteristics. The surface plasma treatments described in the literature mainly aim at achieving anti-fogging properties. The invention has the additional object of providing polymers whose surfaces have a high anti-light scattering effect in order to increase visibility through said polymer. Another aspect of the invention concerns items comprising a hydrophilic polymer surface according to the invention. The items are preferably selected among personal protection equipment, lenses for glasses, visors for helmets, devices for the biomedical field, protection devices for cameras and video cameras, transparent partitions for technical rooms and controlled work environments, solar cells, solar thermal panels, panels for building construction and food packaging. Particularly preferred are lenses for glasses, optical elements or protection devices in the biomedical sector, such as lenses or covers for probes and video cameras. Advantageously, the item that comprises a surface according to the invention is an optical element.

The hydrophilicity of the surface according to the invention is an effect that in the ambient atmosphere (in the air) decreases over time, so that after 7 - 8 days (approx. 200 hours) the values of the contact angle become again equal to those of the non-treated surface.

In order to slow down the increase of the contact angle of the surface according to the invention, post-treatments of the surface are useful, that is, a storage method that makes the (super)hydrophilicity effect of the surface last longer.

Another aspect of the invention thus concerns a storage method of the surface according to the invention or of a surface produced with the process according to the invention or of an item comprising such a surface, wherein said surface or said item is preserved in water. Other suitable storage means are vacuum, an evacuated humid environment, inert liquids or gases such as argon, that is, means protected from the ambient atmosphere.

Table 1 below shows the results obtained with this storage method for a polymer with a surface according to the invention. The contact angle for the polycarbonate/water system shows values below 20° even after 20 and 40 days of storage, respectively: Table 1 : storage in water [days] polymer/water

contact angle [°]

0 (surface just treated with plasma) 5 (± 2)

20 12 (± 3)

40 15 (± 7) Storage in water ensures a considerable improvement compared to storage in the ambient atmosphere. Storage helps maintain a small contact angle until the surface is used.

Variant embodiments of the invention are the subject of the dependent claims. The description of preferred examples of embodiment of the hydrophilic polymer surface, of its production process, of the use of said process and of the items comprising said surfaces according to the invention is provided by way of example without limitation with reference to the attached drawings. Brief description of the drawings

- Figure 1 shows the device used for the combined plasma treatment (cool sputter coater);

- Figure 2 shows the equipment used for measuring the contact angle;

- Figure 3 shows the equipment for the light scattering test;

- Figure 4 shows a diagram representing the contact angle (C.A.) as a function of the treatment time at the pressure of 0.1 Torr;

- Figure 5 shows a diagram representing the contact angle (C.A.) as a function of the treatment pressure for a treatment time of 150 sec;

- Figure 6 shows a diagram representing the contact angle (C.A.) as a function of the exposure time at the pressure of 0.08 Torr;

- Figure 7 shows a diagram representing the contact angle (C.A.) as a function of the treatment power for a treatment time of 150 sec;

- Figure 8 shows the transmittance spectrum as a function of the wavelength for various samples of polycarbonate treated at variable pressures;

- Figure 9 shows the reflectance spectrum as a function of the wavelength for the samples of polycarbonate treated at variable pressures according to

Figure 8;

- Figure 10 shows a diagram representing the contact angle (C.A.) as a function of the presence of AU2O3 for various polycarbonate samples treated at variable pressures;

- Figure 11 shows a diagram representing the contact angle (C.A.) as a function of the presence of nitrogen for various polycarbonate samples treated at variable pressures;

- Figure 12 shows a non-treated PC sample subject to light scattering;

- Figure 13 shows a PC sample treated with plasma at 0.08 Torr not subject to light scattering; - Figure 14 shows the result of the fogging test carried out on the samples shown in Figures 12 and 13;

- Figure 15 shows a non-treated lens of normal safety glasses subject to light scattering;

- Figure 16 shows the lens of Figure 15 treated with plasma at 0.08 Torr not subject to light scattering;

- Figure 17 shows a non-treated lens of safety glasses with anti-fogging properties subject to light scattering;

- Figure 18 shows the lens of Figure 17 treated with plasma at 0.08 Torr not subject to light scattering;

- Figure 19 shows a direct comparison between the results of the fogging tests carried out on the lenses of Figures 15 and 16;

- Figure 20 shows a direct comparison between the results of the fogging test carried out on the lenses of Figures 17 and 18.

Description of the examples of embodiment of the invention

Here below the polymer model taken as preferred polymer is polycarbonate. The choice is not limiting, as also other polymers can be considered, such as polypropylene, polyethylene, polyesters etc. In polycarbonate, transparency and the absence of colour allow very high light transmission through the material, 89% transmittance in the visible spectrum, and furthermore PC is capable of absorbing most of the UV rays. This polymer is used for various applications thanks to its properties like: light weight, high chemical resistance, good resistance to heat, high resistance to friction and transparency. Its optical properties allow the polymer to be used to make lenses for glasses. Its light weight and mechanical resistance allow it to be used to make helmets and panels for the building construction sector.

The treatment on the polymer was performed by means of a sputter coater

POLARON E5100, schematically illustrated in Figure 1.

The machine 2 allows various types of treatment to be carried out, from the deposition of thin films to the surface treatment of a material through plasma.

In order to obtain a cold plasma, in this case a high vacuum system is used.

Vacuum is generated by means of a rotary pump 4. A micrometric valve 6 that regulates a small flow of gas inside the system is used to regulate pressure and obtain the desired value. Pressure control is performed by means of a high vacuum meter 8. Pressure is measured in Torr. The activation and maintenance of the plasma discharge are obtained using a high voltage DC generator, with voltage exceeding one kilovolt. Voltage (kV) (voltage regulator 10) and treatment time in minutes (timer 12) can be set on the generator. Once the desired parameters have been set, the plasma is struck and the current is read (current meter 14). The sample is introduced in the vacuum chamber 16. The type of treatment performed on the polymer is a mixed treatment, that is, partly a plasma treatment and partly a cathode spray. The treatments performed on the polymer are carried out at ambient temperature, the target is constituted by 99.99% pure gold and the gas used ' is air. The tests take place at a voltage of 1.8 kilo Volt (kV) with pressures included between 0.06 and 0.1 Torr for treatment times between 30 and 180 seconds. The same results can be achieved for a wide interval of values of the potential applied to the cathode, an interval preferably ranging between 1.8 kV and 3 kV.

The measurement of the contact angle (Figure 2) is performed by positioning the sample 18 on a support 20 which allows height adjustment (height regulator 22) and small side shifts through a rotation pin 24. The sample is lit with the lamp 26 and one drop of milli-Q water (purified and deionized with resistivity of 18.2 MQxcm) is put on the same using a syringe (usually 2 μΙ). The measurement is performed by means of a camera 28 with a CMOS sensor and a focusing device 30, size 640x480 pixel, to which an optical system with magnifying power up to 30X has been applied. At least four measurements of the contact angle have been acquired for each sample, depositing the same number of drops. The average between the measured values and the error is calculated for each sample through the standard deviation. For non-treated polycarbonate, the result is thus an average value of approximately 83° (standard deviation 2°).

Several optical measurements have been carried out on the samples to verify that the polymers subjected to treatment do not lose their characteristics of transparency in the visible spectrum (approx. 380 nm up to 760 nm). The optical measurements (transmittance and reflectance) have been performed through a V- 670 Jasco UV Vis spectrophotometer.

The polycarbonate sheets (LS151263 NL) used were supplied and guaranteed by the manufacturer (Goodfellow Cambridge CB44DJ England): 10 sheets, 150 mm x 150 mm, thickness 1 mm, density 1.2 g/cm³ and maximum workability temperature 115-130°C. They were cut in small rectangles with size 2 cm x 2.5 cm. In addition to pure polycarbonate, commercial lenses typically used in labs and made with polycarbonate according to standards 2C-1.2 U1 F CE and 2-1.2 U1FN CE were studied. The lenses are separated from the frame and cut in two parts, in such a way as to have two samples for each type of lens. The cutting operation is carried out using gloves, in such a way as to avoid contamination due to direct contact with the hands. Once cut, the samples must be properly cleaned in order to avoid the release of substances at the low pressures to which the samples are subjected during the treatments. They are successively immersed in a beaker containing isopropyl alcohol 99.9% pure which in turn is placed in a water bath for ultrasound treatment for a time interval of 10 minutes. Ultrasound and alcohol combined together eliminate most of the polluting substances. Finally, the samples are dried with nitrogen and then they are ready to be used. For the purposes of the tests some samples are inserted in the Sputter Coater (Polaron E5100) and treated, like others are not treated, so that they can be used for comparison.

For the anti-light scattering test (Figure 3), a led torch 32 was positioned on a support in a dark room and several water drops were deposited on the polymers being examined 34 using a syringe. Each polymer was positioned between the light and an observer 36 with a camera 38. Photographs of the non-treated polymer and of the polymer treated with plasma were made and then compared.

For the anti-fogging test, the treated and the non-treated polymers are put in a fridge for a few minutes, in such a way as to lower their temperature and favour the fogging process. Once they have cooled down, the samples are immediately positioned on a book and subjected to water vapour. The samples are rapidly photographed.

Treatments performed on polycarbonate at a pressure p = 0.1 Torr as a function of the treatment times.

Figure 4 represents the variation of the contact angle (C.A.) as a function of the treatment time at the pressure of 0.1 Torr. The line at approx. 85° represents non-treated polycarbonate. After every treatment performed at the pressure of 0.1 Torr the contact angle is considerably reduced compared to the non-treated polymer (83°): all the treated samples have a contact angle smaller than 20°, therefore the polymer surface that was scarcely hydrophilic becomes highly hydrophilic. It can also be observed that any variation in the treatment time does not involve considerable variations in the contact angle. Treatments performed on polycarbonate for 150 seconds at variable pressure. In the successive treatments the treatment time of 150 seconds was kept constant and the plasma treatment pressure was modified. A treatment time of 150 seconds represents a compromise between sufficiently effective exposure to plasma and exposure that modifies the polymer only superficially. The diagram of Figure 5 represents the measure of the contact angle as a function of the treatment pressure expressed in Torr. All the samples treated with processes performed at different pressures between 0.06 and 0.1 Torr have a contact angle that is smaller than 20°. All the processes thus make the surface highly hydrophilic. The samples treated at a pressure included between 0.06 and 0.1 Torr have an average contact angle of 16°, except for the sample treated at the pressure of 0.08 Torr which has a contact angle smaller than 5° and whose surface is therefore superhydrophilic. These results show that the optimal pressure, meaning the pressure that makes it possible to achieve superhydrophilicity, is equal to 0.08 Torr.

Treatments performed on polycarbonate at the pressure of 0.08 Torr varying the treatment time.

Figure 6 confirms that treatment at this pressure allows an optimal result to be achieved in terms of contact angle, smaller than 10°. In particular, in the samples treated for 120, 150 and 180 seconds a contact angle smaller than or equal to 5° is obtained, and it can be noted that the treatment time practically does not affect the contact angle.

Treatments performed on polycarbonate as a function of the electric power applied to the cathode.

In order to verify the existence of a possible correlation between the contact angle and the treatment power, various treatments were performed varying power and pressure, the results of said treatments being shown in Figure 7 with a treatment time of 50 seconds. In comparison with Figure 4, with a fixed power of 23.4 W, no important variation can be observed. The contact angle does not seem to depend directly on the treatment power. For a superhydrophilic surface to be obtained, there is a preferred treatment pressure and this condition is not correlated with the treatment power.

In addition to the solid-liquid interaction, it is also important that the plasma treatments do not modify the performance of polycarbonate in the UV region and above all that they do not reduce transmittance excessively in the visible. The treatments modify the optical properties of the polymer, the samples treated at different pressures have different colours. Treated polycarbonate tends to become darker as pressure is reduced.

In order to verify that the polymers treated at different pressures do not show considerable transparency reductions in the visible spectrum, optical transmittance and reflectance measurements were performed. A treatment time of 120 seconds was chosen for the optical tests. The selected value represents an intermediate time that ensures sufficient exposure of the samples to plasma and preserves the surfaces from excessive degradation due to the treatment. The results are shown in Figures 8 and 9. Figures 8 and 9 respectively represent the transmittance and reflectance spectrum as a function of the wavelength in the wavelength interval from UV radiation (350 nm) to the end of the visible spectrum (750 nm).

The measurements were made on samples treated at different pressures. Furthermore, a non-treated polycarbonate was taken as reference for the measurement. In the ultraviolet band (350-400 nm) transmittance for all samples is equal to zero. Therefore, the treatments do not reduce the capacity of the polycarbonate used as a substrate to absorb most of the UV rays. Non-treated PC has a visible light transmittance of 89%. The polymers treated at a pressure of 0.1 and 0.08 Torr have good transmittance in the visible interval, equal to approximately 75%. The transmittance of PC treated at a pressure of 0.06 Torr, instead, is lower than 60%. The polycarbonate which gives the best results in terms of transmittance and contact angle is thus the sample treated at a pressure of 0.08 Torr. The transmittance and reflectance measurements show how light, which is not transmitted by the samples, is divided in absorbed light and reflected light. It can be observed that all the treated samples have higher reflectance than polycarbonate. The reduced transmittance highlighted in the diagram of Figure 8 is thus mainly due to the increased reflectance. The surface treated at a pressure of 0.06 Torr, in fact, reflects approximately 23% of the visible light, while the samples treated at 0.08 and 0.1 Torr reflect much less light, approximately 15% of the visible light. The increase in reflectance might be caused by the presence of gold on the polymer surface. The gold deposited on the surface does not create a continuous film on any sample, in fact the electrical measurements made show a completely insulating surface. It is presumed that the surface modification caused by the plasma and the presence of gold particles due to the sputtering process combined together determine the condition of superhydrophilicity. XPS analyses were performed on the samples in order to verify the presence of functional groups and the presence of metal induced by plasma. Table 2 below shows the chemical composition of non-treated polycarbonate, of samples treated at different pressures and the polycarbonate values to be found in the literature. XPS analysis is a semi-quantitative analysis and the values of the elements are expressed as percentage values.

Table 2

The results show that the treatment causes modifications on all the treated samples. Compared to pure polycarbonate, in fact, the treated samples contain nitrogen. The table shows a decrease in carbon for the treated samples, while there is a strong increase in oxygen. The presence of gold on the surface is confirmed by the XPS analyses that show the presence of gold, for a quantity of approximately 30%, in all the treated samples. Part of the XPS signal connected to the presence of gold is due to metallic gold (Au) and another part is due to gold oxide (AU2O3). The sample treated at a pressure of 0.08 Torr contains a high quantity of gold oxide and nitrogen.

In the light of these results it can be understood that the applied process is partly a process of surface modification induced by plasma and partly a process of gold particle deposition. For the samples treated at 0.06 Torr and 0.1 Torr the different percentages of gold in the form of gold oxide or of nitrogen do not affect the contact angle, which is always of approximately 15°. For the sample treated at the pressure of 0.08 Torr, the presence of a considerable quantity of gold oxide and nitrogen seems to have a direct correlation with the contact angle < 5° (Figures 10 and 11).

Ageing studies have shown that the high concentration of nitrogen in the sample treated at 0.08 Torr is not responsible for the reduction of the contact angle compared to the non-treated sample. The non-aged sample has a contact angle smaller than 5°, while the aged sample has a contact angle similar to that of the non-treated sample (over 80°).

Table 3 compares the XPS analysis of polycarbonate treated at 0.08 Torr in the aged and non-aged condition: Table 3

The percentage of nitrogen between the two samples is not subject to particular variations. On the other hand, the presence of gold is subject to considerable variations. In particular, metallic gold increases from 19.35% to 22,91% while gold oxide decreases considerably, from 11.25% to 2.79%. Considering that nitrogen is not subject to particular variations and given the considerable reduction in gold oxide, it can be inferred that the characteristic of superhydrophilicity is closely related to the presence of gold oxide. The experiments carried out up to now have shown that the treatment is very effective and considerably reduces the solid-liquid interaction of the treated samples, in particular, at the pressure of 0.08 Torr it is possible to obtain the condition of superhydrophilicity, preserving a good level of light transmittance. The wettability measurements, the optical measurements and the results of the XPS have shown that the treatment carried out on the surfaces is partly due to the modification caused by the interaction between plasma and polycarbonate and partly to the deposition of gold particles on the surface.

In order to verify the effectiveness of the plasma treatment, the anti-light scattering test and the anti-fogging test were performed both on the sample with superhydrophilic surface and on the non-treated polycarbonate. Figures 12 to 14 show the photographs of the anti-light scattering test and of the anti-fogging test performed as described above. Figure 12 shows the photograph of the anti-light scattering test carried out on non-treated polycarbonate. The image behind the sample is not clear, and in particular the water drops present on the surface tend to diffuse the light of the light source. This generates a series of secundary light spots that disturbs the perception of the image behind the sample. In the treated polymer with superhydrophilic surface the image that can be seen through the polycarbonate is clear (Figure 13), thanks to the reduction of light scattering induced by the water drops. Regarding the anti-fogging test, the photograph in Figure 14 shows how the portion of the underlying page is legible with the treated sample while the page is illegible with the non-treated sample due to the fogging phenomenon.

The plasma treatment at 0.08 Torr for 120 seconds was applied also to real protection devices. The test was carried out on the lenses of two different lab glasses made in polycarbonate: polycarbonate lenses according to standard 2C-1.2 U1 F CE and polycarbonate lenses according to standard 2-1.2 U1 FN CE.

The first sample is a pair of protection glasses in polycarbonate, while the second sample is again a pair of glasses in polycarbonate for which the manufacturer declared that they were in compliance with the anti-fogging standards. The contact angle of the non-treated lenses and of the same lenses subjected to the plasma treatment was measured for both devices. The measurements of the contact angle made on the treated and on the non- treated lenses are shown in Table 4. Table 4

Table 4 shows that the lenses have smaller contact angles compared to pure polycarbonate. The plasma treatment results to be effective also on the lenses of the devices, in fact both of them have a contact angle smaller than 5° after the plasma treatment. The anti-light scattering test and the anti-fogging test were carried out on both lenses of the devices. Figures 15-16 show the photographs of the anti-light scattering test performed on the lenses of the device in compliance with standard 2C-1.2 U1 F CE, treated and non-treated. For the non-treated lens, the image behind the lens is not clear, and in particular the water drops present on the surface tend to diffuse the light of the light source. This generates a series of spots of secondary lights that disturbs the perception of the image behind the lens. In the treated lens with superhydrophilic surface the image that can be seen through the polycarbonate is clear, thanks to the absence of the light scattering effect induced by the water drops.

Figures 17 and 18 show the photographs of the anti-light scattering test performed on the lenses of the device in compliance with the 2-1.2 U1 FN CE standard. Figure 17 shows the photograph of the non-treated lens; as in the previous case, the non-treated lens is subject to the light scattering effect induced by the drops on the surface. Figure 18 shows how this phenomenon does not appear on the same lens when this has been treated.

Figures 19 and 20 show the anti-fogging tests carried out on lens 2C-1.2 U1 F CE (Figure 19) and on lens 2-1.2 U1 FN CE (Figure 20). The images show that the underlying page portion is legible with the treated lens. The non-treated lens behaves in a different manner, in fact the underlying page is illegible due to the fogging phenomenon.

The tests showed the effectiveness of the plasma treatment on the lenses of both of the personal protection devices. This implies that superhydrophilic surfaces are less subject to light scattering and fogging phenomena thanks to the formation of a water film due to the flattening of the drops. Light can pass through the structure consisting of polycarbonate and water without trajectory deviations, maintaining the perception of the image.

The invention achieves the object to provide a hydrophilic polymer surface and - in the case of treatment at 0.08 Torr - a superhydrophilic polymer surface with good anti-fogging and anti-light scattering properties without affecting the characteristics of high transmittance of the polymer. Furthermore, the invention achieves the object to provide a method for producing such a surface and the use of the process for producing surfaces with anti-light scattering properties. Upon implementation, the hydrophilic polymer surface, the process for production of the same, the use and the items comprising said hydrophilic surface of the invention can be subjected to further modifications or variants not described herein. Said modifications or variants must all be considered protected by the present patent, provided that they fall within the scope of the following claims.

Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the protection of each element identified by way of example by such reference signs.

Claims

1) Hydrophilic polymer surface, preferably having a contact angle smaller than 20°, characterized in that the surface comprises gold.

2) Surface according to claim 1), characterized in that said gold is at least partially present in the form of gold oxide.

3) Surface according to claim 1) or 2), characterized in that said hydrophilic surface was created by means of a plasma treatment in combination with a cathode spray with a gold target.

4) Surface according to any of the preceding claims, characterized in that the polymer is polycarbonate.

5) Surface according to any of the claims from 1) to 4), characterized in that the contact angle with water is < 20°, preferably < 5°.

6) Surface according to claim 5), wherein the contact angle is determined with a water drop approx. 2 μΙ in volume placed on said surface.

7) Surface according to any of the claims from 2) to 6), characterized in that gold oxide is AU2O3.

8) Surface according to any of the claims from 2) to 7), characterized in that the atomic percentage of gold in the form of oxide exceeds 10% as determined with XPS (X-ray photoelectric spectroscopy) analysis.

9) Surface according to any of the claims from 2) to 8), characterized in that gold is present both in the metallic form and in the form of gold oxide.

10) Surface according to any of the preceding claims, characterized in that the total gold atomic percentage determined through XPS (X-ray photoelectric spectroscopy) is preferably of approximately 30%.

11) Process for making a hydrophilic polymer surface preferably having a contact angle smaller than 20°, comprising the following steps:

a) preparation of a polymer surface;

b) preferably cleaning of the polymer surface;

12) Process according to claim 11), characterized in that said plasma is a cold plasma and the gas used in the plasma treatment is air.

13) Process according to claim 11) or 12), characterized in that said plasma treatment with cathode spray is performed at pressures included between 0.06 and 0.1 Torr, preferably at 0.08 Torr. 14) Process according to any of the claims from 11) to 13), characterized in that said plasma treatment with cathode spray is performed during time intervals included between 30 and 180 seconds, preferably time intervals included between 120 and 150 seconds.

15) Use of the process according to any of the claims from 11) to 14), intended to give optical elements, on the surface, anti-fogging and anti-light scattering characteristics.

16) Item comprising a hydrophilic polymer surface according to any of the claims from 1) to 10).

17) Item according to claim 16), characterized in that it is selected among personal protection equipment, lenses for glasses, visors for helmets, devices for the biomedical field, protection devices for cameras and video cameras, transparent partitions for technical rooms and controlled work environments, solar cells, solar thermal panels, panels for the sectors of building construction and food packaging.

18) Item according to claim 16), characterized in that it is an optical element.

19) Method for storing the surface according to any of the claims from 1) to 10), or the surface produced according to any of the claims from 11) to 14), or an item according to any of the claims from 16) to 18), wherein said surface or said item is preserved so that it is protected from the ambient atmosphere, in particular in water, vacuum, an inert gas or liquid.