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deposited coatings are also low because of the low molecular network connectivity.To achieve coatings with better mechanical properties, we recently demonstrated an atmospheric plasma enhanced deposition technique for depositing transparent organosilicate coatings on plastic substrates with tunable mechanical properties. [9][10][11][12] The optimized bilayer coatings exhibited a twofold increase in adhesion energy with poly(methyl methacrylate) (PMMA) and a three-to fivefold improvement in surface hardness compared to the commercial sol-gel polysiloxane coatings. However, the debond interface still remained adhesively at the polymer and coating interface. Coatings with better adhesive properties which can drive cracks to propagate cohesively within the polymer substrate are highly desirable as it can provide better reliability and durability.In this study, we show the successful deposition of a bilayer protective coating on plastics using a combined spray and atmospheric plasma deposition method. A thin highly adhesive inorganic-organic hybrid coating on plastics was deposited using (3-glycidyloxypropyl) trimethoxysilane (GPTMS) and tetrapropyl zirconate (TPOZ) as precursors with spray coating deposition in air. Among different solution-based processing methods, spray deposition is highly desirable for making large-area, uniform coatings on various kinds of substrates through a simple and cost-effective process. [13] It is also able to coat complex 3D microstructures such as cantilevers and nonplanar surfaces for microelectromechanical systems applications. [14,15] It relies less on solution characteristics than substrate-contact based techniques and provides more flexibility on solvent choice, making it a more versatile process with less environment pollution. [16] Once hydrolyzed, the GPTMS precursor can form an inorganic molecular network via condensation reaction and an organic network via epoxide opening polymerization reaction. TPOZ precursor works as an effective catalyst to the epoxide opening reaction [17][18][19] and also acts as an inorganic network former to increase the inorganic network connectivity of the hybrid coating. After curing of the bottom spray layer, a hard top layer was deposited with atmospheric plasma deposition using tetraethyl orthosilicate (TEOS) as the precursor.The successful processing of bilayer protective coatings on plastics using a combined spray and atmospheric plasma deposition method is shown. The base layer is a spray deposited coating with high adhesion using (3-glycidyloxypropyl) trimethoxysilane and tetrapropyl zirconate (TPOZ) precursors. The top dense layer is deposited by atmospheric plasma deposition with a tetraethyl orthosilicate precursor. The coating deposition rate, chemical composition, elastic modulus, hardness, and adhesion to poly(methyl methacrylate) (PMMA) substrates are investigated. The adhesion to the polymer substrate is found to decrease with increasing TPOZ content in the precursor solution, while the elastic modulus and hardness of the base layer ...

A polymeric gel contains a crosslinked polymer network and solvent. Gels can swell or shrink in response to external stimuli. Two typical kinetic processes are involved during the deformation of gels: the viscoelastic and poroelastic responses. Viscoelasticity of gels is generated from local rearrangement of the polymers, while poroelasticity is generated from solvent migration. The coupled time-dependent behaviors of gels can be formulated by coupling a spring-dashpot model with a diffusion–deformation model. Different combinations of spring and dashpot and different ways of dealing with the coupling between solvent migration and rheological models—either through the spring or dashpot—induce significantly different constitutive behaviors and characteristic time-dependent responses of gels. In this work, we quantitatively study how different rheological models coupled with solvent migration affect the transient behavior of gels. We formulate the visco-poroelastic gel theory for the Maxwell model, the Kelvin–Voigt model, and the generalized standard viscoelastic model. In addition, for generalized standard viscoelastic model, we also discuss the different coupling through the secondary spring or the dashpot. The models are implemented into finite element codes, and the transient-state simulations are performed to investigate the time-dependent deformation and frequency-dependent energy dissipation of different rheologically implemented gel models. The result shows that different combinations of spring and dashpot give the gel solid-like properties and liquid-like properties under different time scales; in addition, the coupling of solvent migration with the dashpot in the rheological model results in restrictions of solvent migration under certain length scales.

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