Patent Application: US-201514734520-A

Abstract:
a substrate subject to degradation at temperatures above 100 ° c . is coated with a nanostructured ceramic coating having a thickness in excess of 100 nm , formed on a surface of the substrate , wherein a process temperature for deposition of the nanostructured coating does not exceed 90 ° c . the coating may be photocatalytic , photovoltaic , or piezoelectric . the coating , when moistened and exposed to ultraviolet light or sunlight , advantageously generates free radicals , which may be biocidal , deodorizing , or assist in degradation of surface deposits on the substrate after use . the substrate may be biological or organic , and may have a metallic or conductive intermediate layer .

Description:
general procedures of precursor solution preparation and titania film deposition are discussed in g . zhang , b . k . roy , l . f . allard , and j . cho , “ titanium oxide nanoparticles precipitated from low - temperature aqueous solutions : ii . thin - film formation and microstructure developments ,” j . am . ceram . soc ., 93 [ 7 ] 1909 - 15 ( 2010 ), expressly incorporated herein by reference . a preferred method for coating a plastic item is as follows . the surface of the plastic , which may have a mold release composition or other residual coating on it , is first cleaned , for example with freshly prepared piranha cleaning solution , i . e ., h 2 o 2 and sulfuric acid . a typical mixture is 3 : 1 concentrated sulfuric acid to 30 % hydrogen peroxide solution , though a range of 2 : 1 to 7 : 1 may be used . cleaning is conducted for 1 - 10 minutes at an appropriate temperature below 100 ° c ., e . g ., 60 - 90 ° c ., though care is exercised to avoid significantly degrading the substrate , and the cleaning is ceased as soon as the surface is uniformly wetted and clean . the substrate is then dried in dry nitrogen gas ( n 2 ) blow , and treated with an o 2 plasma ( harrick plasma , ithaca , n . y .) for 15 min to render the surface hydrophilic . a desired amount of hydrochloric acid ( hcl , 36 . 5 %- 38 %, j . t . baker , phillipsburg , n . j .) was first dissolved in ice - cold di water ( barnsted e - pure , resistivity 18 - 20 mω - cm ) followed by slow injection of adequate amount of titanium chloride ( ticl 4 , 99 . 99 %, alfa - aesar , ward hill , mass .) in a parafilm - covered glass bottle for supersaturation . the method for calculating supersaturation at the deposition temperature is addressed in g . zhang , b . k . roy , l . f . allard , and j . cho , “ titanium oxide nanoparticles precipitated from low - temperature aqueous solutions : i . nucleation , growth , and aggregation ,” j . am . ceram . soc ., 91 [ 2 ] 3875 - 82 ( 2008 ), expressly incorporated herein by reference . once prepared , the solutions were kept refrigerated until utilized . the substrates may be seeded , by coating with compatible nanocrystals , such as by spin coating ( e . g ., for flat surfaces ) or dipping in a seeding solution . the substrates are then placed in a beaker containing freshly prepared precursor solution . the beaker was placed in an oil - bath , preset at 60 - 90 ° c ., to perform the deposition . the ph of the solution is maintained by addition of a suitable acid , such as hcl for ticl 4 ( ph & lt ; 1 . 5 ). the process is preferably conducted at temperatures below 90 ° c ., both to avoid damage to the substrate , and because the low temperature maintains a slow reaction rate and higher quality smaller crystals . as temperature increases , the reaction rate increases , and larger crystals with higher crystallinity result . the coating may be facilitated by an electrochemical process . the substrate is selected as one which is inherently conductive , or coated with a conductive surface , such as a metal . in this case , hydrogen peroxide is added to the precursor solution , for example , 10 mm hydrogen peroxide in 5 mm ticl 4 in 3 : 1 methanol - di water . for example , the substrate is held at a cathodic deposition potential , with current held at a level which does not result in apparent hydrogen generation ( bubbling ), which might reduce coating quality . for example , the cathode voltage is held between about − 3v to − 5v with respect to a platinum foil reference electrode ( anode ) in the solution . ph and voltage may be adjusted to control both hydrogen bubble formation and corrosion of the conductive substrate . see , biplab k . roy , guangneng zhang , roy magnuson , mark poliks , and junghyun cho , “ electrodeposition of titania thin films on metallic surface for high - k dielectric applications ”, j . am . ceram . soc ., 93 [ 3 ] 774 - 781 ( 2010 ), expressly incorporated herein by reference . the deposition is conducted to produce a coating of the desired thickness , and may be monitored by ph change ( and amount of acid needed to titrate the solution to maintain ph ), time and electrical current , etc ., or by mechanical or functional measurements . the precursor solution is changed at every hour to increase the deposition rate and to avoid any heavy particle agglomeration . the surface morphology and crystallinity of the resulting thin films can be controlled by changing solution parameters . a thermodynamic parameter , supersaturation ( s ), has been identified as a key controlling factor to tailor such variations . after desired deposition periods , films were cleaned with ethanol and dried under mild n 2 blow . titania particles form electrochemical conversion of ticl 4 to tio 2 in the solution , via thermal - energy - driven homogeneous nucleation . the thin film formation occurs by attraction and assembly of nanoparticles on substrate surface . precursor solution environment not only determines the nanoparticle assembly and the film microstructure , but also influences the phase of titania ( amorphous , anatase , or rutile ). films obtained from very low s (˜ 63 . 9 ) solution typically have a distinct “ leaf - like ”- structured surface morphology , with traces of anisotropic structured growth extending from the substrate surface to the top edge of the film . growth rates in low s precursor are higher than in high s precursor . with increasing supersaturation ( i . e ., s ˜ 232 . 8 ), bulk precipitation becomes more dominant with less contribution toward film formation and hence , the film growth rate decreases . a low s solution contains more hcl and less ticl4 . increased hcl imparts a common ion ( cl −) effect and prevents dissociation of ticl4 , and low supersaturation can therefore be achieved . in this process , high s solution inherently has higher ph , whereas low s solution shows lower ph . three phases of titania ( namely rutile , anatase , and amorphous ) are formed . at very high supersaturation , the rate of hydrolysis is much faster than condensation . this situation can lead to random polycondensation of hydrolyzed octahedra and generation of amorphous phase . therefore , at higher supersaturations , anatase phase surrounded primarily with amorphous titania is obtained . amorphous phase content increases with increase in supersaturation and leads to the formation of denser and smoother film morphology . in contrast , low s conditions primarily produced directed rutile - type crystalline growth and porous films with rough topology . although anatase and rutile crystals can be observed in the deposited films , the presence of amorphous phase cannot be ignored in overall film morphology . due to rapid hydrolysis characteristics of ti 4 + , even in very controlled deposition conditions , polycrystalline films contain an amorphous phase along with nanocrystalline particles . therefore , in all situations , it is important to realize the composite nature of the films with some dominating phases . from low s precursors , rutile phase appears as a dominant one . as the supersaturation increases , the anatase phase first dominates in the film structure and the amorphous phase becomes prevalent at even higher supersaturations . in low s deposited rutile - containing films , porosity and segmented structure of aligned plates limits is evident . the optical absorption spectrum of rutile films obtained from low s solution is markedly different from that of films obtained from higher supersaturations . highly acidic low - supersaturation solutions produce a rutile - type of crystallinity and porous morphology , whereas the higher supersaturation results in the formation of amorphous and anatase phase with a denser microstructure . uv - vis studies reveal a distinct difference in the optical absorptions between films formed from low s and high s ticl 4 precursor solutions . the rutile - based films displayed a lower optical band gap than the films containing anatase / amorphous phases . due to their densely packed particulate structure , the films obtained from high s showed higher mechanical properties than the porous rutile films . dielectric properties of the rutile films were , however , superior to the anatase / amorphous films because of significant difference in dielectric constants among amorphous , anatase , and rutile phases . this offers a way of tuning thin film dielectric properties by manipulating the phase evolution with controlled solution parameters . the photoelectrochemical response is higher for the rutile - containing films , attributable to higher porosity ( leading to more dye absorption , higher interaction area ), higher refractive index , better crystallinity , and larger thickness of the low s generated films compared to their high s counterparts . zinc oxide ( zno ) films consisting of vertically aligned nanorods may be hydrothermally grown on a seed layer at e . g ., 90 ° c . using two alternate precursors ( zinc acetate , zinc nitrate ). vertically grown nanorods exhibit the ( 002 ) out - of - plane texture and their size , alignment , density , and growth rate can be controlled by both solution and seed layer conditions . a continuous or stepwise deposition may be implemented . a seed layer , e . g ., znac 2 may be deposited and cured at temperatures as low as 100 ° c . in - situ precipitated nanoparticles and nanostructures from aqueous solution are provided . see , sunghee lee , biplab kumar roy , and junghyun cho , “ vertically aligned zno nanorods grown by low - temperature solution processing ”, japanese journal of applied physics 52 ( 2013 ) 05da09 , expressly incorporated herein by reference . zinc oxide ( zno ) is a direct wide band gap ( 3 . 4 ev ) semiconductor , which is comparable to tio 2 , while having several advantages over tio 2 such as easy crystallization at low temperature , 1d anisotropic growth , and high electron mobility . a hydrothermal process to produce the film employs low process temperatures , which permit use of flexible polymer substrates . compared to other solution - based techniques which utilize open bath , the hydrothermal processing provides high controllability of nanostructures because of the mild deposition condition resulting from the higher solubility of zinc ions that , for example , titanium ions . vertically aligned nanorods or nanotubes have shown some advantages over the nanoparticle clustered structures for enhanced photovoltaic ( pv ) properties due to their faster electron transport and reduced charge recombination . a seed layer may be provided to assist in in aligning the nanorod structure on the substrate . the surface of the plastic substrate , which may have a mold release composition or other residual coating on it , is first cleaned , for example with freshly prepared piranha cleaning solution , i . e ., h 2 o 2 and sulfuric acid . a typical mixture is 3 : 1 concentrated sulfuric acid to 30 % hydrogen peroxide solution , though a range of 2 : 1 to 7 : 1 may be used . cleaning is conducted for 1 - 10 minutes at appropriate temperature , though care is exercised to avoid significantly degrading the substrate , and the cleaning is ceased after the surface is uniformly wetted and clean . the substrate is then dried in dry nitrogen gas ( n 2 ) blow , and treated with an o 2 plasma ( hayrick plasma , ithaca , n . y .) for 15 min to render the surface hydrophilic . the treated substrate can be coated with a thin layer of a 1 : 1 molar ratio of zinc acetate dihydrate and ethanolamine in 2 - methoxyethanol ( all three from alfa aesar ), in a concentration range of e . g ., 50 mm - 750 mm , though other concentrations may be employed as appropriate . the solutions may be pre - heated at 60 ° c . for 40 min in a water bath before coating , and cured at less than 90 - 100 ° c . on the seed layer , zno films may be grown by hydrothermal deposition . two types of precursors may , for example , be used : i ) 20 mm zinc acetate dihydrate and 20 mm hexamethylenetetramine ( hmt ; alfa aesar ); ii ) 25 mm zinc nitrate hexahydrate ( alfa aesar ) and 25 mm hmt aqueous solution . seed layer coated substrate is immersed into the precursor solution . the deposition may be conducted at 60 - 90 ° c . the deposition may be , for example , 2 - 8 hours , and may be repeated to build up layer thickness and density . for example , 4 2 - hour sessions may be conducted with a gentle wash and solution replacement between each deposition . during the hydrothermal deposition , bulk precipitates may form , in the precursor solution , and therefore the solution may be replaced with a freshly prepared solution every 1 - 2 h . a hydrothermal spray coating process is also possible , in which particles are formed in a hot supersaturated solution and sprayed with force on an object , to provide a mechanical impact effect to facilitate agglomeration of particles at the surface of the substrate . the solution can be allowed to dry after spraying . in a spray coating embodiment , it is useful to maintain the substrate at elevated temperature , e . g ., 60 - 90 ° c . after the hydrothermal deposition , the zno films were rinsed with deionized water , and blow dried with nitrogen gas . synthetic oxide films in aqueous solution are formed under an accelerated hydrolysis environment for a relatively short period . such hydrolysis process of precursor species strongly depends solution parameters such as ph , concentration and temperature . the solubility of the oxides and their hydroxides need not be known , and the thermodynamics data may be used to calculate equilibrium solubility for the stable phases , from which the degree of supersaturation s can be calculated . it provides the driving force for nucleation and growth of the oxide nanostructures . g . zhang , b . k . roy , l . f . allard , and j . cho : j . am . ceram . soc . 91 ( 2008 ) 3875 . depending on the availability of oh — ( i . e ., with ph of solution ) the extent of hydrolysis may vary . in the zn — oh system , soluble species of zn ( ii ) ions include zn 2 + , zn ( oh ) + , zn ( oh ) 2 , zn ( oh ) 3 − , and zn ( oh ) 4 2 − . a preliminary calculation indicated that s at ph 7 or lower is extremely small compared to that of ti — oh , and therefore a complexing agent such as hmt ( c 6 h 12 n 4 ) or dimethylamine borane [ dmab , bh 3 nh ( ch 3 ) 2 ] is provided to assist in precipitating a zno phase . due to the complexing agent , zn 2 + cation also forms amine complexes such as zn ( nh 3 ) 4 2 + with nh 3 ( aq ) in moderately basic solution . a higher degree of supersaturation s can be attained either by increasing temperature or by increasing ph of the solution , so subsequent precipitation can be accelerated . the nanorods from a zinc acetate precursor solution tend to show straighter and more densely packed structure while those from a zinc nitrate precursor are less vertically aligned and less dense . the morphological difference between the films produced by different precursors is likely due to different ph values of the solutions . the initial ph values for the zinc acetate based precursor and the zinc nitrate based precursor are , for example 6 . 95 and 6 . 82 , respectively . the difference in ph over 0 . 1 can in fact make a significant change in terms of the degree of supersaturation , which is the driving force for nucleation and growth of the zno nanorod . therefore , high ph in the case of zinc acetate precursor will yield more nucleation density for zno rods and make them more packed and straight during the growth . the effects of ionic species generated from different precursors alters the stabilization of the rod surfaces ( particularly , basal plane vs non - basal planes ); by inactivating non - basal planes ( m - planes ) through ion attachment , the aspect ratio can increase and the rod growth can be faster . nanorod films may have a thickness range , for example , from 350 to 1700 nm , without cracks or film delamination . a polymeric substrate in the form of a molded , extruded , or formed useful article , subject to degradation by extended temperatures in excess of 100 ° c . is provided . the substrate is initially prepared to ensure a hydrophilic surface . for example , the article may be immersed or coated with piranha cleaning solution ( h 2 o 2 and sulfuric acid ), for a sufficient time to fully clean the surface , but the process is limited to avoid substantial damage to the article . the substrate is then dried and may be treated with oxygen plasma to render the surface hydrophilic . in some cases , the surface may be masked , either to selectively produce hydrophilic properties , or to subsequently block the surface , to produce a latent pattern . the substrate is , for example , formed from polyethylene terephthalate ( pet ), peek , polyurethane , nylon , epoxides , polyamides , polyaramides , polyvinyl chloride , polystyrene , abs ( acrylonitrile and styrene , toughened with polybutadiene ), polyethylene , polypropylene , polycarbonate , teflon ® or other fluoropolymer , silicone , silicone heteropolymer or copolymer , etc . rubbers and elastomers may also be treated . films and panes , especially optically transmissive structures , may be employed as well . the useful article is , for example , a kitchen utensil , an eating utensil ( knife , fork , spoon ), kitchenware ( plate , bowl , cup ), tray , table , headboard , cutting board , spatula , container , plastic flatware , serving dish , toothbrush , hair brush , or the like . the useful article can also be a disposable medical device , such as a catheter , intravenous line , suture , or other transcutaneous or patient - contact device , or simply an item provided in the patient room , recovery room , operating or procedure room . the substrate , which may be pre - seeded , is immersed in a supersaturated solution of ceramic precursor , and the supersaturated solution may be replenished after some period of deposition with an acid having the same counterions as the ceramic precursor cations , to maintain supersaturated deposition conditions . process temperatures are maintained below a softening temperature of the molded useful article , i . e ., below 100 ° c ., and preferably below 90 ° c . throughout the process . the deposition proceeds for 2 - 8 hours with the precursor solution replaced every 2 hours , to form a layer of zno nanorods e . g ., 1 , 000 nm thick , and preferably in the range 250 - 3 , 000 nm thick . a low density polyethylene mixed with polyisobutene ( pib ) or poly [ ethylene - vinylacetate ] ( eva ) copolymer 40 - 100 gage , biaxially oriented monolayer film is provided . one surface of the film is treated with an oxygen plasma to increase hydrophilicity . the hydrophilic surface is immersed in a supersaturated ceramic precursor solution , to selectively coat the hydrophilic surface with a nanostructured ceramic coating 100 - 350 nm thick . the resulting product is a ceramic - coated asymmetric cling wrap , with a sticky side and a ceramic coated side . the ceramic coating reduces permability to oxygen and water , increases handleability , and provides photocatalytic properties . the process conditions are maintained below 100 ° c . because of the tight radii that such a film may be subjected to , it is likely that the ceramic coating will suffer cracks if used as a traditional cling wrap . however , portions of the film that are not bent or crushed , should display a high ratio of photocatalysitc activity to weight , and may be used to provide a temporary photocatalytic surface . a wood product , such as a cutting board , is provided . the wood is treated to ensure hydrophilicity , such as by acid or base , short piranha treatment , enzymatic treatment , or the like , and optionally an oxygen plasma treatment . the wood is kiln dried at 100 ° c . and surface of the wood is saturated with 1 : 1 zinc acetate : and ethanolamine in 2 - methoxyethanol , and then dried at 100 ° c . to leave crystal seeds . the wood product is then immersed in a supersaturated solution of aqueous 20 mm zinc acetate / 20 mm hexamethylenetetramine for two hours or more . the resulting product has a surface which is impregnated and coated with zno ceramic nanorods . it is noted that under ultraviolet illumination , with moisture , hydroxyl radicals and hydrogen peroxide are generated , which will tend to degrade the wood , but also degrade odors , food residue , and bacteria . the lignin in the wood is relatively resistant to oxidation , and therefore the reduction in product life is acceptable . a woven or non - woven fabric , such as a natural fiber , such as cotton , or linen , or a synthetic fiber such as polyester , nylon , rayon , pet , polyethylene , or the like is provided . depending on the fiber type , the substrate is treated to ensure a high degree of hydroxylation , such as by an acid treatment and / or oxygen plasma treatment . hydrophobic substrates formed of non - porous fibers , such as ultra high molecular weight polyethylene , may be treated with piranha . the hydrophilic substrate is saturated with 1 : 1 zinc acetate : and ethanolamine in 2 - methoxyethanol , and then dried at 100 ° c . to leave crystal seeds . the seeded substrate is then immersed in a supersaturated solution of aqueous 20 mm zinc acetate / 20 mm hexamethylenetetramine for two to eight hours . the resulting product has a surface which is impregnated with zno ceramic nanoparticles . the fabric may , prior to coating , be formed into a useful article such as drapes or other window treatments . under ultraviolet illumination , in the presence of moisture , hydroxyl radicals and hydrogen peroxide are generated , which will render the drapes hung in a window or as a room divider in hospital room settings as an air cleaner , to reduce odor tend to reduce bacterial growth and aerosol transfer . metallized plastic silverware or a metallized plastic cell phone case is provided . see , u . s . pat . nos . 8 , 621 , 755 , 8 , 176 , 641 , 6 , 983 , 542 , 5 , 280 , 052 , 5 , 177 , 124 . the substrate is prepared by treatment with oxygen plasma to render the surface hydrophilic . a coating is formed by an electrochemical deposition process . the ceramic precursor solution includes 10 mm hydrogen peroxide in 5 mm ticl 4 in 3 : 1 methanol - di water . the substrate is held at a cathodic deposition potential , and maintained at a ph and voltage potential to avoid corrosion of the metallized coating and also avoid hydrogen bubbling , while driving formation of a ceramic coating . a coating is formed as a single layer or in a series of layers , for example 30 seconds applied potential , 30 seconds altered potential ( preferably , a cathodic protection potential for the metalized film ) for 4 cycles , to form a ceramic layer of 250 - 1 , 000 nm . it is to be understood that while a certain form of the invention is illustrated , it is not to be limited to the specific form or arrangement herein described and shown . it will be apparent to those skilled in the art that various changes may be made without departing from the scope of the invention and the invention is not to be considered limited to what is shown and described in the specification and any drawings / figures included herein . the embodiments , methods , procedures and techniques described herein are presently representative of the preferred embodiments , are intended to be exemplary and are not intended as limitations on the scope . changes therein and other uses will occur to those skilled in the art which are encompassed within the spirit of the invention and are defined by the scope of the appended claims . all patents and publications mentioned in this specification are expressly incorporated herein by reference in their entirety , 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