B. K. Kim

Organic–inorganic nanocomposite bilayers with triple shape memory effect

Various amounts of silica nanoparticles were chemically incorporated into amorphous polyurethanes (PU) of two different molecular weights by sol–gel reactions, and the effects were studied in terms of mechanical, dynamic mechanical, dual, and triple shape memory effects (DSME and TSME) of the nanocomposite films. It was found that the silica particles act as multifunctional cross-links as well as reinforcing fillers and significantly augmented the glassy and rubbery state moduli, yield strength, break strength, glass transition temperature, and dual shape memory properties. A cohesive bilayer of the two films fabricated from an interpenetrating polymer network (IPN) exhibited synergistic mechanical properties in the glassy and rubbery states along with two undisturbed glass transitions by which an intermediate plateau region and TSME were demonstrated.

Effect of polymer structure on the morphology and electro-optic properties of UV curable PNLCs

Abstract Polymer network liquid crystals (PNLC) were prepared from UV curable polyurethane acrylate (PUA) and a nematic liquid crystal mixture (E7) at a fixed film composition of 1.5/8.5 (polymer/LC) by weight. The polymer networks were obtained upon curing the reactive mixture of hydroxyethyl acrylate (HEA) terminated polyurethane prepolymer, monoacrylate and triacrylate (4/3/3). The effects of prepolymer molecular structure viz., length of polyurethane (PU) segment, molecular weight (Mn) and functionality (f) of polyol(PPG), and type of hard segment were studied in terms of morphology, voltage–transmittance relationship, off-state transmittance–temperature relationship, and thermal properties of the films. Aromatic diisocyanate (TDI) segment of PU showed greater chemical affinity with aromatic LC molecules and gave smaller domain size resulting in higher threshold (V10) and driving (V90) voltages. The increase in prepolymer molecular weight gave larger polymer–LC phase separation and decreased V10 as well as V90, together with smaller nematic–isotropic transition temperature depression. Increase in functionality and decrease in Mn of PPG gave smaller domain size, smaller decay time, greater V10 and V90, longer rise time, and greater depression of TNI in film.

SHAPE MEMORY BEHAVIOR OF AMORPHOUS POLYURETHANES

Amorphous polyurethane (PU)–based shape memory polymers (SMPs) were synthesized with different extents of allophanate reactions, hard segment contents, and types of polyol. They were characterized in terms of hydrogen bonding, mechanical, dynamic mechanical, and thermomechanical properties of solution-cast films. Polyols with molecular mass of 500 g/mole resulted in two-phase mixed morphology of the PU. However, the extent of phase mixing depended on the cross-linking density and hard segment content, as well as the type of polyol, and was directly related to the hydrogen bonding determined from the Fourier transform infrared (FTIR) measurements.

Optimization of holographic polymer dispersed liquid crystal for ternary monomers

Polarized optical micrography (POM) images of gratings and UV-visible spectra of holographic polymer dispersed liquid crystals (HPDLC) are reported for a ternary monomer system composed of dipentaerythritol hydroxypentaacrylate/trimethylolpropanetriacrylate/N-vinylpyrrolidone (DPHPA/TMPTA/NVP) = 7/2/1 by weight. Gratings were written by irradiation with an argon ion laser (λ = 488nm) at various intensities (20-200mWcm -2 ) on monomer/liquid crystal (LC) composite films of various compositions (75125, 70/30, 65135, 62138, 60/40). Reflection efficiency-irradiation intensity-film composition relationships are obtained in three dimensional plots which show that maximum reflection moves from high LC content (38%) at low irradiation intensity (20mWcm -2 ) to low LC content (25wt%) at high irradiation intensity (200mWcm -2 ).

Synthesis and Properties of Thermosensitive Poly(N-Isopropylacrylamide)/Waterborne Polyurethane Graded Concentration Hybrid Films

Temperature-sensitive hybrid films were synthesized with a concentration gradient by casting and UV curing of N-isopropylacrylamide (NIPAAm) monomers (0%–70%) on the free surface of waterborne polyurethane (WPU) films on a Teflon substrate. The surface hardness and contact angle of the free surface with a water drop increased asymptotically with the addition of NIPAAm, whereas those on the substrate side were virtually unchanged. The diffusion coefficient (D), rates of swelling at 20°C (below the lower critical solution temperature (LCST) of poly(N-isopropylacrylamide) (PNIPAM)) and deswelling at 50°C (above the LCST) increased with increasing NIPAM content, showing favorable thermosensitivity. In addition, the glassy state modulus and glass transition temperature (Tg) of the film increased with increasing NIPAM content, whereas the rubbery modulus decreased due to the increased molecular weight between the crosslinks. In addition, as the NIPAM content increased, the film showed a positive yield with an increased yield and fracture stress and decreased ductility. Above 50% NIPAM, the film became brittle, showing a linear stress–strain relationship.

Triple shape-memory effect by silanized polyurethane/silane-functionalized graphene oxide nanocomposites bilayer

Graphene oxide (GO) was chemically modified with 3-aminopropyltriethoxysilane (APTES) (f-GO) and incorporated into silanized polyurethanes of two different molecular weights and chemical compositions by sol–gel reactions, and the effects were studied in terms of mechanical, dynamic mechanical, and dual and triple shape-memory polymers (DSMP and TSMP, respectively) of the nanocomposite films. It was found that the f-GO nanoparticles act as multifunctional cross-links as well as reinforcing fillers and significantly augmented the glassy and rubbery state moduli, yield strength, break strength, glass transition temperature, and dual shape-memory properties. A cohesive bilayer of the two films (lower layer and upper layer) fabricated by the interpenetrating polymer network technique exhibited synergistic mechanical properties in the glassy and rubbery states along with two undisturbed glass transitions by which an intermediate plateau region and TSMP were demonstrated.

Mechanical, Thermal, and Surface Properties of Ultrahigh Molecular Weight Polyethylene/Polypropylene Blends

Various compositions of ultrahigh molecular weight polyethylene/polypropylene (UHMWPE/PP) blends were prepared in decalin, with the rheological, mechanical, thermal, and surface properties of the blends being determined using the solution cast film. Viscosity and mechanical properties of the blends decreased below the additivity value with increasing PP content implying that PP molecules disturb the entanglement of UHMWPE. Contact angle of the blend films with a water drop increased with increasing content of PP. The atomic force microscope (AFM) images showed that the surface of cast UHMWPE was very smooth whereas that of cast PP was very uneven. For blends, the surface became rough and uneven with increasing content of PP. The melting temperature of PP (T mP) decreased in the blends with increasing UHMWPE content while that of UHMWPE (T mU) remained almost constant in blends.

Biodegradable Holographic Polymer-Dispersed Liquid Crystal

The a-D-glucose was chemically modified with an allyl isocyanate (MG) and introduced into the polymer matrix for holographic polymer-dispersed liquid crystal (HPDLC), and the effects were studied in terms of morphology, grating formulation dynamics and electro-optical and biodegradable properties. Phase separation and diffraction efficiency increased at low content of (MG ≤ 4 wt%), while a rapid increase in crosslink density entrapped the LC droplets within the polymer to give poor phase separation, small droplet size, and low diffraction efficiency at high content. The HPDLC film was driven only with the addition of MG due to the increased droplet size with a minimum driving voltage of 18 V at 6.0 wt% MG. With the addition and an increasing amount of MG, the biodegradation of the composite film in a buffer solution was significantly increased in proportion to its amount.

An Analysis and Visualization System for Ship Structural Intensity Using a General Purpose FEA Program

The structural intensity analysis, which calculates vibration energy flow from vibratory velocity and internal force of a structure, can give information on sources` power, dominant transmission path and sink of vibration energy. In this study, we present a system for structural intensity analysis and visualization to apply for anti-vibration design of ship structures. The system calculates structural intensity from the results of forced vibration analysis and visualize the intensity using a general purpose finite element analysis program MSC/Nastran and its pre- and post-processor program. To demonstrate the analysis and visualization capability of the presented system, we show and discuss the results of structural intensity analysis for a cross-stiffened plate and a 70,500 OW crude oil tanker

Natural Vibration Analysis for Stiffened Plate of Ship Tank Side in Contact with Water Using Assumed Mode Method

In this study, the assumed mode method using characteristic polynomials of Timoshenko beam is applied to the free vibration analysis for the stiffened plate of ship tank side in contact with water. The hydro-elastic effect of the fluid-structure interaction is considered by fluid velocity potential, derived from boundary conditions for fluid and structure, and utilized in the calculation of added mass matrix using assumed modes. To verify the validity and effectiveness of the presented method, free vibration analysis for the stiffened plates in contact with finite and infinite fluids have been carried out and its results were compared with those obtained by a general purpose FEA software.