Regular Surface Relief Research Articles

Photo-Induced Relief in Rheology of Liquid Crystals

In this paper, we report the first experimental results on capillary shear flows of a nematic liquid crystal 5CB (4-cyano-4′-pentylbiphenyl), arising due to interaction of the anisotropic liquid, correspondent to the continuous rotational symmetry, with photo-profiled polymer surfaces. The regular surface relief was obtained due to opto-mechanical deformation of azobenzene containing potoresponsive polymer film (PAZO) during irradiation with two-beam interference. Such surface treatment makes it possible to obtain a regular submicron profile with well-defined characteristics (direction, period, and height). The polarizing microscopy (PM) and dynamic light scattering (DLS) techniques were used to determine the direction of the surface orientation of LC and anchoring strength, which characterize the interaction of LC with the photo-profiled polymer surface. Two types of shear flows—spreading of LC droplets and capillary flow in a plane capillary, induced by the interaction of LC with one or two photo-profiled surfaces—were investigated for different directions of the flow relative to the direction of the relief. Strong anisotropy in the dynamics of the precursor film and contact line motion, as well as in the dynamical contact angle, was established. The experimental results were analyzed and compared with those previously obtained at the investigation of the spreading of LC droplets over a mechanically stamped submicron profile and capillary flows in plane capillaries with photo-aligned surfaces.

Adhesive Interaction of Elastic Bodies with Regular Surface Relief

This paper focuses on adhesive interaction between an axisymmetric indenter and an elastic half-space taking into account the surface microrelief in the form of regularly located identical asperities covering the indenter. The microlevel contact between the asperities system and the elastic half-space is considered discrete. The solution to the problem at the macrolevel is constructed using the dependence of the effective specific adhesion force on the value of the nominal gap obtained by solving the problem at the microlevel. The constructed solution makes it possible to model the influence of microgeometry and adhesion parameters on the contact interaction of elastic bodies at the macrolevel.

Polyisobutylene-Based Thermoplastic Elastomers for Manufacturing Polymeric Heart Valve Leaflets: In Vitro and In Vivo Results

Superior polymers represent a promising alternative to mechanical and biological materials commonly used for manufacturing artificial heart valves. The study is aimed at assessing poly(styrene-block-isobutylene-block-styrene) (SIBS) properties and comparing them with polytetrafluoroethylene (Gore-texTM, a reference sample). Surface topography of both materials was evaluated with scanning electron microscopy and atomic force microscopy. The mechanical properties were measured under uniaxial tension. The water contact angle was estimated to evaluate hydrophilicity/hydrophobicity of the study samples. Materials’ hemocompatibility was evaluated using cell lines (Ea.hy 926), donor blood, and in vivo. SIBS possess a regular surface relief. It is hydrophobic and has lower strength as compared to Gore-texTM (3.51 MPa vs. 13.2/23.8 MPa). SIBS and Gore-texTM have similar hemocompatibility (hemolysis, adhesion, and platelet aggregation). The subcutaneous rat implantation reports that SIBS has a lower tendency towards calcification (0.39 mg/g) compared with Gore-texTM (1.29 mg/g). SIBS is a highly hemocompatible material with a promising potential for manufacturing heart valve leaflets, but its mechanical properties require further improvements. The possible options include the reinforcement with nanofillers and introductions of new chains in its structure.

Liquid crystal and photo-induced properties of polymers carrying pyridylazobenzene groups and iodopentafluorobenzene rings self-assembled through halogen bond

In this work, we report on the synthesis, liquid crystal behavior and photo-induced optical properties of a polymer and a copolymer, both carrying lateral pyridylazobenzene groups and iodopentafluorobenzene (IPFB) rings self-assembled through halogen bond. The formation of the halogen-bonded complexes was confirmed by Fourier transform infrared (FTIR) spectroscopy; the mesomorphic behavior was determined by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and X-ray diffraction (XRD); and the optical properties were photo-induced with a 405 nm laser beam. The pyridylazobenzene-functionalized polymer showed a smectic-type order (smectic A and crystE phases) whereas the copolymer and the halogen-bonded complexes with IPFB rings formed aggregates whose molecular order in the z-coordinates is suppressed (no layers). The photo-isomerization (in solution) of the polymer and copolymer led to a trans-to-cis isomer conversion (%cis) of 82, and 95, respectively. In film, the %cis values resulted much inferior but still high enough to induce optical properties, as for instance, in films of the copolymer (%cis = 60) and its halogen-bonded complex (%cis = 46) that responded quite well in periodical light-induced writing/erasure experiments. Only the halogen-bonded copolymer complex allowed us to register regular surface relief gratings (SRGs) suggesting that it would be a good candidate for optical data storage applications.

Means for Giving Flexibility to a Laser Beam Tool

Background. Existing opinion of laser ray, as universal instrument, so justly, as far as judgment is faithful that a metal-cutting instrument is universal. Universality is confirmed by instrument functionality, and the compared objects in this sense are practically equal. A difference is in that a metal-cutting instrument is created beforehand, including its special kinds, while a laser ray becomes an instrument in the moment of its use. The latter both complicates and simplifies work of technologist – his fantasy is unlimited, modernization and size modification of chart and construction of instrument are possible, even during a technological operation. It can be attained because of unique property of laser ray – his flexibility.Objective. Knowledge of this ray property does not guarantee its successful application, because it is not enough to use the known optical elements and their charts for transformation of ray to the effective and various instrument. Herein there is the aim of the paper – by unconventional and sometimes unobvious technological and designer decisions to show hidden possibilities of laser ray, as a flexible instrument.Methods. Principal incentive reason of diverse instrument creation is a necessity of the technological providing of new or set of the known flow sheets of zones of irradiation forming for the different types of treatment: from superficial (engraving, creation of regular surface relief) to the size (precision).Results. For realization of treatment flow sheets range the results of development and use of traditional and original means of laser ray transformation into an instrument (optical elements with changeable parameters, combined systems for the complex affecting of ray purveyance, for expansion of his influence zone, for medicine) are shown.Conclusions. Flexibility of laser ray at converting it into a processing instrument is less as inherent to its property, and more as chance for a technologist to simplify implementation of technological operations and diversify their results.

Combined effect of surface microgeometry and adhesion in normal and sliding contacts of elastic bodies

In this study, models are proposed to analyze the combined effect of surface microgeometry and adhesion on the load–distance dependence and energy dissipation in an approach–separation cycle, as well as on the formation and rupture of adhesive bridges during friction. The models are based on the Maugis–Dugdale approximation in normal and frictional (sliding and rolling) contacts of elastic bodies with regular surface relief. For the normal adhesive contact of surfaces with regular relief, an analytical solution, which takes into account the mutual effect of asperities, is presented. The contribution of adhesive hysteresis into the sliding and rolling friction forces is calculated for various values of nominal pressure, parameters of microgeometry, and adhesion.

Effect of External Electric Field on Diffraction Efficiency of Polarized Holograms in Films of 4-[(2-Nitrophenyl)Diazenyl]Phenyl Methacrylate Copolymer With Octyl Methacrylate

Holograms with a plane wavefront for parallel and orthogonal orientation of polarization of the light beams were obtained in films of the 4-[(2-nitrophenyl)diazenyl]phenyl methacrylate copolymer with octyl methacrylate, and the effect of an external electric field on their diffraction efficiency was investigated. Two effects from the electric field on the diffraction efficiency of the reconstructed holograms were observed: a fast effect leading to decrease of the diffraction efficiency and a slow effect leading to increase of the diffraction efficiency in the reconstructed holograms. The mechanism of formation of the latent holographic image and the effect of the external electric field on it are due not to the photosemiconducting properties of the films but to optical anisotropy in the isomers of the azobenzene groups and the formation of regular surface relief in the films.

Vibrational stability of metal-cutting machines with modified frictional conditions in the slipping guides

Electromechanical hardening with the formation of regular surface relief in the lathe guides is considered.

Sapphire substrates with a regular surface relief

The lithography-free technique is proposed to obtain a regular relief in the form of a regular 2D system of 25-nm protrusions on a sapphire plate surface. The use of grid masks allows one to form a regular relief on the sapphire substrates of arbitrary area. The structure of crystal films formed by the sputtering of metal aluminum onto sapphire substrates with subsequent oxidation and annealing is thoroughly investigated and compared with the nanostructured (0001) sapphire wafer surface in the form of regular steps up to 5 nm in height with atomically smooth terraces.

Fabrication of Photoprocessible Azo Polymer Microwires through a Soft Lithographic Approach

In this work, a soft lithographic approach has been developed to fabricate free-standing azo polymer microwires with unique photoprocessible characteristics. In the process, an epoxy-based azo polymer (BP-AZ-CA) was used to prepare both the soft lithographic masters and the microwires. The masters were prepared by photofabricating surface relief gratings on BP-AZ-CA thin films. Then the elastomeric stamps were prepared by replica molding of poly(dimethylsiloxane) prepolymer against the masters. With use of the stamps and a solution of BP-AZ-CA as "ink", the microwires were prepared by contact printing and wet etching. The microwires possessed a uniform sub-micrometer-scale transverse dimension and macroscopic longitudinal dimension. Those characteristic sizes depended on the adjustable features of the masters and stamps used in the process. The transverse dimension of the microwires could be altered after exposure to a linearly polarized Ar+ laser single beam with the polarization direction perpendicular to the longitudinal axes of the microwires. Upon irradiation of interfering p-polarized Ar+ laser beams, regular surface relief structures could be inscribed on the microwires along the longitudinal direction, which coincided with both the polarization direction of the laser beams and the grating vector direction of the interference pattern. The microwires with photoprocessible properties are potentially usable as sub-micrometer-scale materials in future miniaturized components and devices. The approach reported in this work can be further extended to the fabrication of nano-/microwires from other polymeric materials.

Rotational Reorganization of Doped Cholesteric Liquid Crystalline Films

In this paper an unprecedented rotational reorganization of cholesteric liquid crystalline films is described. This rotational reorganization results from the conversion of a chiral molecular motor dopant to an isomer with a different helical twisting power, leading to a change in the cholesteric pitch. The direction of this reorganization is correlated to the sign of the change in helical twisting power of the dopant. The rotational reorganization of the liquid crystalline film was used to rotate microscopic objects 4 orders of magnitude larger than the bistable dopants in the film, which shows that molecular motors and switches can perform work. The surface of the doped cholesteric liquid crystalline films was found to possess a regular surface relief, whose periodicity coincides with typical cholesteric polygonal line textures. These surface features originate from the cholesteric superstructure in the liquid crystalline film, which in turn is the result of the presence of the chiral dopant. As such, the presence of the dopant is expressed in these distinct surface structures. A possible mechanism at the origin of the rotational reorganization of liquid crystalline films and the cholesteric surface relief is discussed.

Submicron photomanipulation of self-assembled polydiacetylenes

A new class of soluble, processable polydiacetylenes(PDA) derived from the alkoxycarbonylmethyl-and related urethanes of 9-(aryl-5, 7-nonadiyn-1-ol has been designed and synthesized. The aryl groups used include N-methyl-anilino, diphenylamino, and 9-carbazolyl. These PDA are susceptible to postpolymerization functionalization via the aryiamine and ester groups. Examples of the former include tricyanovinylation and diazonium salt coupling. The latter materials are the first rigid rod polymers to allow direct photofabrication of regular surface relief gratings, as revealed by atomic force microscopy(AFM).

Self-Assembling Functionalizable Polydiacetylenes and their Optical Properties

AbstractThe alkoxycarbonylmethylurethanes of 9-(N-methyl-N-phenylamino)-5,7-nonadiyn-l-ol were synthesized and polymerized by 60Co gamma radiation. The resulting polydiacetylenes (PDA) are soluble, processable, and self-assemble into an acentric array. These PDAs are susceptible to postpolymerization functionalization via its dialkylaniline and ester groups, and hence comprise the most versatile PDA system for systematic chemical modification reported to date. Dialkylaniline functionalization via tetracyanoethylene and diazonium salt coupling led, respectively, to materials with interesting second order nonlinear optical properties and that exhibit directly photofabricated regular surface relief gratings. The latter materials provide the first example of a rigid rod polymer (lacking a detectable glass transition) to exhibit such phenomena. Moreover, these PDAs can form self-assembled multilayer structure in water by ester hydrolysis.