Delicate Modification of Poly(dimethylsiloxane) Ultrathin Film by Low-Energy Ion Beam Treatment for Durable Intermediate Liquid Crystal Pretilt Angles

Abstract

Long-term stability of intermediate liquid crystal pretilt angles on a poly(dimethylsiloxane) (PDMS) ultrathin film grafted onto a surface was realized simply and easily via low-energy ion beam (IB) treatment. The composition and surface energy of the thin film could be controlled by varying the low-energy IB treatment. This treatment results in the permanent chemical modification of the film surface, converting it from organic PDMS to a mixed layer of organic PDMS and inorganic silica. The partial transformation of a PDMS surface gives rise to the control of the pretilt angle via the formation of the inhomogeneous surface and the stabilization of the pretilt angle via the cross-linking reaction of broken chemical bonds through IB irradiation. As a result, a continuous variation of pretilt angles that maintained their initial value with long-term stability was obtained. Thus, the unique chemical transformation of the PDMS surface using IB treatment may allow for the production of durable intermediate liquid crystal pretilt angles.

Optofluidics based on liquid crystal microflows

“…The origin of this observation is that the E7 constituents contain non-polar alkyl tails. PDMS is also hydrophobic and as a result the E7 NLC will align perpendicularly due to the wetting properties of the boundary conditions [19,[27][28][29]. PDMS thus forms an elegant platform where cost-effective 'pixelation' can take place by replica-molding, while the self-assembly of the NLC requires no surface pre-treatment.…”

Fabrication of a Multidomain and Ultrafast‐Switching Liquid Crystal Alignment Layer Using Contact Printing with a Poly(dimethylsiloxane) Stamp

“…PDMS typically has a lower surface energy than general LC molecules, which means that LCs are easily aligned vertically on a substrate surface 11. Therefore, this principle of LC alignment depending on surface energy does not allow a plausible interpretation of the planar homogeneous alignment on the PDMS SAO layer as fabricated by the contact printing and peeling method in this study.…”

“…For this PDMS thin film layer with a randomly coiled conformation, the LC alignment direction was perpendicular to the surface and vertical LC behavior was exhibited (as shown in the left‐hand inset of Figure 2d), because of nonpolar intermolecular interaction between the terminal methyl (–CH 3 ) groups of randomly coiled chains and the side chains of the LC molecules. Indeed, the intrinsic properties of a general PDMS thin layer induce the vertical LC configuration 11, 22. However, the PDMS SAO alignment layer showed a planar homogeneous alignment of the LCs (as shown in the left‐hand inset of Figure 2f).…”

“…In LC display applications, LC molecules must be skillfully controlled for the desired alignment states, ranging from a planar to vertical state having a preferred direction or disclination in the spatial LC medium 7. To date, an additional alignment layer with functional materials such as polymers,8 amorphous metal oxides,9–11 or anisotropic nanostructures12, 13 is required for precise control of LC alignment states on isotropic substrates such as indium tin oxide (ITO), silicon wafer, glass, and polymers. However, the additional alignment layers, which are placed between the LC medium and substrate, often lead to degradation of the overall performance of the LC display device, for example, with a decrease in transmittance arising from the thickness of the alignment layer, which is a few hundred nanometers, and the mismatch of refractive index between the respective media.…”

Polymer‐Layer‐Free Alignment for Fast Switching Nematic Liquid Crystals by Multifunctional Nanostructured Substrate

“…It is important to note that pretilt angle control of nematic LC molecules using surface nanostructures on electrode is a new phenomenon. In all previous studies, pretilt angle control was accomplished by using physical and chemical methods such as rubbing and photoalignment . In these procedures, which require the use of polymer alignment layers, control of pretilt angles is achieved by changing the length of the polymer side chain, the strength and depth of rubbing, surface hydrophobicity, the curing temperature and film thickness .…”