Hyo Kang

Liquid crystal alignment behavior on sulfonated poly(arylene ether sulfone) films

A series of sulfonated poly(arylene ether sulfone) (PAES#, # is the feed monomer ratio of 3,3′-disulfonate-4,4′-dichlorodiphenylsulfone) derivatives were synthesized via nucleophilic addition to investigate the liquid crystal (LC) alignment property of these polymer films. These polymer films exhibited good optical transparency in the visible light region (400–700 nm). For example, the transmittance value (about 96%) of the PAES# film onto a glass substrate at 550 nm is better than that (about 90%) of the polyimide film, the most commonly used LC alignment layer. The LC cells made from the rubbed PAES# films showed a homogeneous planar LC alignment with parallel direction with respect to the rubbing direction. LC cells having pretilt angles from approximately 3° for twisted nematic (TN) to 0° for planar switching mode were obtained from these PAES# films having molar contents of sulfonate groups in the range of 0 to 70 mol%, respectively. The electro-optical characteristics of the LC cells fabricated with the PAES# films such as applying voltage and response time were as good as those fabricated from rubbed polyimide films. We also found that the LC cells made from PAES# films exhibited good thermal stability.

Effects of low-dose niacin on dyslipidemia and serum phosphorus in patients with chronic kidney disease

Background Niacin supplementation improves dyslipidemia and lowers serum phosphorus levels in patients with chronic kidney disease (CKD). We evaluated whether low-dose niacin supplementation can improve dyslipidemia, lower serum phosphorus levels, and be administered with a low frequency of adverse effects in patients with CKD. Methods We retrospectively analyzed the clinical records of patients with CKD who had taken niacin from January 2009 to June 2011. We excluded patients with CKD stage 1 and 5. We then enrolled 31 patients with CKD who had taken niacin at a fixed dose of 500 mg/day for 6 months. We also randomly selected 30 patients with CKD who had been taking statin for 9 months as a control group. Results Among the 34 patients with CKD who were prescribed niacin, five (14%) complained of adverse effects, and three (8%) discontinued niacin. The proportion of patients in the niacin group who had been taking a statin or omega-3 fatty acids was 67.7% and 48.8%, respectively. In the niacin group, high-density lipoprotein cholesterol level was significantly increased and triglyceride level was significantly decreased at 12 and 24 weeks compared with baseline levels (P<0.05). In the niacin group, phosphorous level (P<0.05) was significantly decreased, and glomerular filtration rate (GFR) was significantly increased (P<0.05) at 24 weeks compared with baseline values. Conclusion Low-dose niacin had a low frequency of adverse effects and also improved dyslipidemia, lowered serum phosphorus level, and increased GFR in patients with CKD. Further studies are needed to evaluate the long-term effects of low-dose niacin for renal progression of CKD.

Liquid crystal alignment behavior on transparent cellulose films

The liquid crystal (LC) alignment properties of LC cells fabricated with plant-based cellulose films were investigated. These carefully prepared polymer films exhibited good optical transparency in the visible light region (400–700 nm). For example, the transmittance value (91%) of the cellulose film on the glass substrate at 550 nm is better than that (89%) of the polyimide film, the most commonly used LC alignment layer. The LC cells made from rubbed cellulose films showed homogeneous planar LC alignment in the parallel direction with respect to the rubbing direction. The electro-optical characteristics of the LC cells fabricated with the cellulose films such as applied voltage and response time were as good as those fabricated from rubbed polyimide films. We also found that the thermal stability of the LC cell made from the cellulose film is better than that of the polyimide film.

Photoalignment Behavior on Polystyrene Films Containing Coumarin Moieties

We synthesized a series of polystyrene derivatives containing coumarin side groups, poly(6-(4-vinylbenzyloxy)coumarin)(P6COU#), where # is the molar content of 6-hydroxycoumarin using polymer modification reaction, in order to study the effect of the 6-hydroxycoumarin side groups on the liquid crystal (LC) alignment properties. The LC alignment behavior of these polymers was investigated using photoalignment method. The LC cells made from photoirradiated P6COU# films exhibited homogeneous planar LC alignment with a pretilt angle of approximately 0°. We found that LC aligning ability of the LC cells made from photoirradiated P6COU# films was affected by the molar content of 6-hydroxycoumarin side groups. For example, the azimuthal anchoring energy of a P6COU80 compared to P6COU25 is about 1 × 10−5 J/m2 and 5 × 10−7 J/m2, respectively. The electro-optical characteristics of the LC cells fabricated with P6COU80 films such as voltage holding ratio and residual DC voltage, threshold voltage, driving voltage, and response time were as good as those fabricated from rubbed polyimide films, the most commonly used LC alignment layers.

Vertical alignment of liquid crystal on tocopherol-substituted polystyrene films

ABSTRACT We synthesised a series of vitamin-based and renewable tocopherol-substituted polystyrene (PTOC#, # = 20, 40, 60, 80 and 100), where # is the molar content of tocopherol moiety, using polymer analogous reactions to investigate their liquid crystal (LC) alignment properties. In general, the LC cell fabricated using the polymer film having a higher molar content of tocopherol side group showed vertical LC alignment behaviour. The vertical alignment (VA) behaviour was well correlated with the surface energy value of these polymer films. For example, VA was observed when the surface energy values of the polymer were smaller than about 35.22 mJ/m2 generated by the nonpolar tocopherol moiety having long and bulky carbon groups. Good electro-optical characteristics, such as voltage holding ratio and residual DC voltage, and aligning stabilities at 200°C and ultraviolet irradiation of 10 J/cm2 were observed for the LC cells fabricated using PTOC100 as a LC alignment layer. Therefore, it was first found that the renewable tocopherol-based materials can produce an eco-friendly vertical LC alignment system. Graphical Abstract

Zwitterionic polymers showing upper critical solution temperature behavior as draw solutes for forward osmosis

We synthesized the zwitterionic homopolymer polysulfobetaine (PBET), which shows upper critical solution temperature (UCST) characteristics, via free radical polymerization in order to investigate its suitability as a draw solute for the forward osmosis (FO) process. The FO and recovery properties of PBET were systematically investigated. The UCST characteristics of the monomer sulfobetaine (BET) were not confirmed, while the UCST of PBET was confirmed to be approximately 40 °C. This result suggests that PBET can be easily recovered from aqueous solutions by cooling them to below the UCST. In an active layer facing feed solution (AL-FS) system containing 20 wt% PBET at a temperature of 50 °C, the water flux and reverse solute flux of PBET were found to be approximately 3.22 LMH and 0.36 gMH, respectively. Thus, we investigated the suitability of homopolymers having UCST characteristics as draw solutes for the FO process for the first time.

Liquid crystal alignment behaviors on capsaicin substituted polystyrene films

We synthesized a series of plant-based capsaincin substituted polystyrene (PCAP#, # = 20, 40, 60, 80, and 100), where # is the molar content of the N-vanillylnonanamide moiety as one of the capsaicin derivatives, using polymer analogous reactions to investigate their liquid crystal (LC) alignment properties. In general, the LC cell fabricated using the polymer film having a higher molar content of N-vanillylnonanamide side groups showed vertical LC alignment behavior. The vertical alignment behavior was well correlated with the surface energy of these polymer films. For example, vertical alignment was observed when the surface energy values of the polymer were smaller than about 29.26 mJ m−2 generated by the nonpolar, long carbon groups. Good electro-optical characteristics, such as voltage holding ratio (VHR) and residual DC voltage (R-DC), and aligning stabilities at 200 °C were observed for the LC cells fabricated using PCAP100 as an eco-friendly LC alignment layer based on renewable capsaicin resource containing polymer films.

Vertical liquid crystal orientation of phytochemical-based oryzanol modified polystyrene

Using plant-derived oryzanol, we synthesized a series of phytochemical-based oryzanol-modified polystyrenes (PORZ#, # = 20, 40, 60, 80, or 100, where # is the mole fraction of the oryzanol moiety) using polymer modification reactions in order to investigate their liquid crystal (LC) orientation behaviors. Generally, an LC cell made from polymer films with a higher mole fraction of the oryzanol side group showed vertical LC orientation behavior. The vertical orientation behavior was strongly correlated with the surface energy of these polymer films. For instance, the vertical orientation was observed when the polymers surface energy, which is influenced by the nonpolar and long carbon groups, was less than about 40.42 mJ m−2. Good electro-optical properties, such as the aligning stabilities at 250 °C and ultraviolet (UV) irradiation of 20 J cm−2, the voltage holding ratio, and the residual DC voltage (R-DC), were observed for the LC cells fabricated using PORZ100 as an eco-friendly LC orientation layer.

LC alignment behaviors on polystyrene blend alignment films

ABSTRACT We prepared blend alignment film based on 4-ethylphenoxymethyl-substituted polystyrene (P4EP) and polystyrene (PS) for liquid crystal (LC) alignment. Stable and uniform LC cells having pretilt angles adjustable from 90o to 0o were obtained from these polystyrene blend films having weight contents of P4EP and PS of 1 and 100 weight %, respectively. The LC alignment behavior was well correlated with the wettability of the polymer films. These polystyrene blends having good solubility in many organic solvents and their films having low process temperature can be candidates for LC alignment layer in the flexible display. This study contributes to the latest efforts to develop new alignment layers for pretilt angle control.

Antibacterial and biocompatible ABA-triblock copolymers containing perfluoropolyether and plant-based cardanol for versatile coating applications

ABA-triblock copolymers (PHCPMF#s, where # is the feed ratio of a monomer to an initiator) were prepared via atom transfer radical polymerization (ATRP), using modified perfluoropolyether (PFPE) as a macroinitiator (Br–PFPE–Br) to form the B block, and 2-hydroxy-3-cardanylpropyl methacrylate (HCPM) as a monomer to form the A blocks. Physically stable and transparent cross-linked PHCPMF# (C-PHCPMF#) films could be prepared on a silicon wafer using spin coating, followed by UV irradiation to form the cross-linked structure. C-PHCPMF# showed bactericidal properties and bacterial adhesion resistance. The bacterial adhesion resistance of the PHCPMF# films was found to closely correlate with the low surface energy and water contact angle hysteresis. In particular, the C-PHCPMF5 film, containing about two HCPM units in the A block, shows excellent biocidal/bacterial adhesion resistance and cell viability because it has an optimum amount of biocidal HCPM units, and a sufficient amount of biocompatible PFPE units to impart a low surface energy.