In nanotechnology, many scientists have been seeking for new functional polymers, which can replica nano-sized features to achieve improved performances of nano-devices. Soft lithography has been widely used in replica of small features as a low cost alternative to conventional UV photolithography. However, commercial silicon rubbers, PDMS polymers, which have been used in current soft lithography, show limitations, especially for nano-resolution soft lithography. These limitations have motivated us to develop a new version of PDMS polymers to overcome those limitations and thus to extend current technology in soft lithography to the advanced level. Since the resolution of soft lithography significantly relies on stamping performance, we designed a novel PDMS prepolymer, which has photocurable cross-linkers to enhance mechanical property to improve lithographic performance and also to create photocurable capability.

Evaporative deposition from a sessile drop is an appealing way to deposit materials on a surface due to the simplicity of the technique. In this work we deposit aqueous solutions of two types of colloidal particles, namely bacteria and microspheres, on mica. We show that by controlling the extent of initial drop spreading through subtle changes in surface conditioning caused by exposure to the laboratory atmosphere in a laminar flow hood it is possible to systematically vary the particle deposition patterns. On freshly cleaved mica the contact angle of water is < 5°. Drops of bacterial and microsphere solutions deposited on freshly cleaved mica spread to cover a large surface area. Drying occurs through pinning and depinning events leaving a series of colloidal particle rings. We found in our laboratory that the contact angle of water on mica exposed to a constant flow of filtered laboratory air in a laminar flow hood gradually increases with time. For drops of both bacterial and microsphere solutions there is a corresponding decrease in the extent of drop spreading with increasing exposure of the mica surface to laboratory air. This results in a profound change in the colloidal particle deposition pattern. Short exposures of minutes to hours are enough to decrease spreading and affect the resulting deposition pattern. For our longest mica surface exposure times (months to 1 year) the contact angle of water reaches values near 20°. Spreading of the bacterial and microsphere drops is substantially decreased. A portion of the colloidal particles are deposited in an outer deposition ring which marks the extent of drop spreading and the remainder of the particles are deposited in the drop interior as a honeycomb or cellular film. The fraction of the drop residue covered with the cellular film increases with particle concentration as well as the length of time the mica is exposed to the laboratory atmosphere. This work shows that evaporative deposition on mica is very sensitive to surface conditioning through atmospheric exposure and also suggests that particle deposition patterns can be tuned by small changes in drop spreading.

Colloidal crystals have been attracting much attention due to their novel use as 3D-photonic crystals and to their structural color. We have been developing a method for the colloidal crystal growth of opal films immersed in silicone oil. This method is one of the evaporative self-assembly techniques for opal films from colloidal particle suspensions. Understanding the mechanism of the process is important to assure the coating of high-quality opal thin films. The colloidal crystallization from suspension was observed with a long working distance optical microscope and Bragg's diffraction peaks were measured with a miniature fiber optic spectrometer. The transition from a non-crystalline to a crystalline phase is observed within a region between the disordered colloidal suspension and the colloidal crystal film. Within this region, that spans a distance of about 400μm, the lattice of the colloidal crystal reduces until it transitions to the close-packed structure.

We present a variation of a standard convective self-assembly technique, where the drying meniscus is restricted by a straight-edge located approximately 100 μm above the substrate adjacent to the drying zone. We find this technique to yield films at roughly twice the growth rate compared to the standard technique. We attribute this to differing local evaporation rates in the two cases. We also investigate how the crystal growth rate depends on ambient relative humidity and find a clear linear dependency, which we attribute to the length of the drying zone being constant over a wide range of humidities.

In this work, we report on the evaporative deposition of bacteria from a drying aqueous drop on mica as a function of the bacterial suspension age. For sufficiently aged bacterial suspensions, residues are small and more filled-in than residues formed from fresh suspensions on similarly aged mica. In addition, the interior deposition pattern transitions from a cellular film characteristic of fresh suspensions to a cracked carpet pattern for aged suspensions. Suspension aging related changes in the residues are attributed to accumulation of organic materials such as DNA, RNA, proteins, and other bacterial components in the suspension. The aging process is also observed to be at least partially dependent on ventilation of the suspension during aging.

We demonstrate that deposition patterns formed during drying droplets of aqueous protein solutions are complex, characteristic, and highly reproducible. Substrate, buffer as well as protein type are important factors largely influencing the patterned structure. Specifically, multiple growth zones in what we refer to as “soccer ball pattern” are formed when a droplet of albumin solution in sodium bicarbonate buffer is dried. Each growth zone has periodically patterned, concentric ringed structures surrounding a core at the center. Different macroscopic patterns are also found for streptavidin, fibrinogen, IgG antibody as well as rhodamine B base and polystyrene beads when droplets of their aqueous solutions are dried on the substrates with different degrees of hydrophilicity/hydrophobicity. Furthermore, distinguishable deposition patterns are formed in drying droplets of aqueous protein solutions containing albumin and fibrinogen at different ratios, suggesting that even the relative abundance of multiple proteins influences the deposition patterns. Since the protein pattern is reproducible for a given protein and variable among different proteins, the protein patterns from drying droplets might be useful to potentially identify a given protein under specific conditions.