Process Study Of Particle Replication In Non-wetting Templates

In the realm of nanometer materials, scientists have been devoted into exploring amethod to produce nanoparticles with controlled microstructures, morphology, size andcomposition. A novel method called PRINT （Particle Replication In Non-wettingTemplates） can be used to design and prepare the template with patterns that have thedesired size and shape of the particles through the low surface energyperfluoropolyether （PFPE） material. By the confined space of template, size andshape–specific arrays of polymeric and inorganic particles could be fabricated. Theprocess of PRINT technology consists of three major steps: hard template fabrication,soft template fabrication and printing of particles. Firstly, silicon hard template iscreated through the modern photolithography technology. Secondly, a photocurablePFPE precursor is cast onto the hard patterned template to cure and produce anelastomeric polymer mold. Finally, the soft template is pressed onto the solid solutionlayer of particle material to allow it entering into the cavities, and excess solution isexpelled out due to the low surface energy of soft template. When the material in thecavities is solidified, the desired mono-dispersed size-specific particles are producedafter demolding from the soft template. In this thesis, the focus of our work was mainlyon the synthesis and property study of PFPE material, and establishment of the particleprinting experimental conditions and the effects of process conditions on the quality ofproduced particles.Firstly, we successfully synthesized the PFPE-DMA、PFPE-HMDI-DMA（2:1）、PFPE-HMDI-DMA（3:2）prepolymers with different molecular weights and doublebond terminal groups based on hydroxyl-terminated PFPE, using hexamethylenediisocyanate as chain extender and isocyano ethyl methacrylate as chain end cappingagent.¹H-NMR、¹⁹F-NMR、IR measurements demonstrated that the chemical structuresof the prepolymers were as expected and the products have high purity and few residues.DSC measurements indicated that the three prepolymers were amorphous at roomtemperature, and the viscosity at30oC increased with increasing the molecular weightof the prepolymer. Secondly, the curing conditions of soft PFPE template were investigated and theeffect of molecular weight of the prepolymer on the properties of cured films wasstudied. Surface contact angle measurements indicated that the three films were bothhydrophobic and oleophobic, implying the ease of demolding, and had similar contactangles irrespective of the molecular weight of the prepolymer. Tensile tests showed thatwith the increase of molecular weight of the prepolymer, the elongation to breakincreased, while the tensile strength and modulus decreased. The chain-extendedPFPE-HMDI-DMA （2:1） and PFPE-HMDI-DMA（3:2）films that demonstrated goodflexibility are promising suitable materials to fabricate soft template.Thirdly, the hard template engraved with six groups of particle patterns withdifferent size and shape was fabricated using modern photolithography technology on a4inches silicon wafer. The particle patterns were clear with no defects on the lines andhad high resolution, but the sizes of the patterns were a bit smaller than the designedvalues. The patterns copied onto the soft template resemble the original ones on the hardtemplate, and the size and shape were identical for the same group of particle patterns.However, the three dimensional sizes of particle patterns were much smaller than thoseon the hard template, possibly due to the release of inner energy stored during thecuring process of the soft template.Finally, the printing conditions for PRINT technology were studied using PLA asprinted material and PFPE-HMDI-DMA（3:2）as soft template, and mono-dispersedPLA particles with different sizes and morphology were successfully fabricated. Opticalmicroscopy and confocal laser microscopy measurements indicated that, the generatedparticles have good morphology and identical size, implying the potential value ofPRINT technology.