Jongyoon Kim

Study on in vitro release patterns of fentanyl-loaded PLGA microspheres.

In order to study the development of the delivery device of long-acting local anaesthetics for post-operative analgesia and control of chronic pain of cancer patient, fentanyl loaded poly(l-lactide-co-glycolide) (PLGA, molecular weight; 5000, 8000, 20,000, and 33,000 g/mole) microspheres (FMS) were studied. FMS were prepared by an emulsion solvent-evaporation method. The influence of several preparation parameters such as initial drug loading, PLGA concentrations, emulsifier concentrations, oil phase volume and mole ratio and molecular weight has been investigated on the fentanyl release patterns. Generally, the drug showed the biphasic release patterns, with an initial diffusion followed by a lag period before the onset of the degradation phase, but there were no lag times in the device. Fentanyl was slowly released from FMS over 10 days in vitro, with a quasi-zero order property. The release rate increased with increasing drug loading as well as increasing polymer concentration with a relatively small initial burst effect. From the results, FMS may be a good formulation to deliver the anaesthesia for the treatment of chronic pain.

Dependence of image flickering of negative dielectric anisotropy liquid crystal on the flexoelectric coefficient ratio and the interdigitated electrode structure

We experimentally measured the splay (e s) and the bend flexoelectric coefficients (e b) of liquid crystal (LC) mixtures with negative dielectric anisotropy and investigated their effect on the image flicker of the LC mixtures driven with a low frequency electric field. Using the experimentally measured e s and e b, we simulated the transmittance (TR) response with the continuum model. First, we confirmed that the TR simulation results were approximated to the experimental data with only small variation. Second, we varied the simulation parameters of e s , e b, the separation (S), and the width (W) of the interdigitated electrodes and tried to find the optimum condition showing the least image flicker. Given W = 3.0 μm and e b = 5.7 pC m−1, it was found that the image flicker could be minimized when the e s /e b value was about 2.4 and the S/W ratio was about 1.5. Because the e s /e b value of the rod-like LC material is generally less than 1, it is desirable to design an interdigitated electrode structure to minimize the image flicker effect.

Dielectric relaxation in a novel tapered chiral photochromatic liquid crystalline dendrimer

ABSTRACT Temperature-dependent dielectric spectroscopic measurements of newly synthesised ribbon-shaped chiral liquid crystalline dendrimer with photochromic azobenzene mesogens and an isosorbide chiral centre on planar anchoring cell have been performed in the frequency range of 1.0 Hz to 5.5 MHz. Three dielectric dispersions in the relaxation frequency range of 10–80 Hz, 80–130 kHz and ~3.5 MHz have been observed not only in chiral smectic phase but also in isotropic phase in which two lower-frequency processes are retarded while the other one remained at same relaxation rate from isotropic to chiral smectic phase. Based on the dielectric and optical polarising microscopic results, the chiral smectic phase has been identified as SmC* phase. The relaxation mode observed at low-frequency region in the SmC* phase followed the dielectric characteristics of pinned Goldstone mode. Whereas the dielectric dispersions observed at high-frequency region have been analysed in the framework of the model given by Maier and Meier. GRAPHICAL ABSTRACT

Effect of the ratio between monoacrylate and diacrylate reactive mesogen on the transmission spectrum of polymer-stabilized cholesteric liquid crystal

We investigated the effect of the relative ratio between the diacrylate (DA) and the monoacrylate (MA) reactive mesogen (RM) molecules on the transmission spectrum of polymer-stabilized cholesteric liquid crystal (PSCLC). The reflection color from the top substrate where the UV was exposed was shifted from red to green with increasing the fraction of DA. It was also found that the PSCLC sample with the fraction of DA over 5 wt% formed 2-dimensional poly-grain textures on the bottom substrate. The periodicity of the grains was about 1-2 μm with the consequence of a light-scattering optical texture of the PSCLC sample. By optimizing the relative fraction between MA and DA, we could obtain a vivid broadband PSCLC sample without a scattering of light.

Enhancement of flexoelectric ratio of nematic liquid crystal by doping calamitic ferroelectric liquid crystal

ABSTRACT We measured the flexoelectric ratio e* of a nematic liquid crystal (NLC) doped with a calamitic ferroelectric liquid crystal (FLC). We doped two kinds of commercial FLC into the pure NLC at a weight concentration of 5 wt%. The absolute value of the flexoelectric ratio was increased up to 49% compared to the pure NLC. The greater transverse dipole moment and the elastic constant of FLC are thought to be related to the increase of the flexoelectric ratio. Graphical Abstract

Dependence of the birefringence of polystyrene film on the stretching conditions

We investigated the dependence of the birefringence of polystyrene (PS) film with a negative optical birefringence on the stretching conditions. We varied the stretching ratio (SR), stretching speed (SS), and stretching temperature (ST), and measured the inplane birefringence and the Nz coefficient of the PS film. The inplane birefringence was increased with greater SR and SS but decreased with greater ST. The Nz coefficient of the stretched PS film was around zero and showed similar dependence on the stretching conditions like inplane birefringence.

Broadening the reflection bandwidth of polymer-stabilized cholesteric liquid crystal via a reactive surface coating layer

We report a method of broadening the reflection bandwidth of polymer-stabilized cholesteric liquid crystal (PSCLC). The top substrate was consecutively coated with a polyimide (PI) and a reactive mesogen (RM) layer, while the bottom substrate was coated with only PI. We exposed the top substrate with the RM coating to UV light. The reflection bandwidth of the PSCLC samples where the top substrate was over-coated with RM was significantly broader than the samples where both substrates were coated with PI. In addition to the effect of the UV intensity gradient, the RM-coated top substrate has a chemical affinity to bulk RM, promoting formation of the pitch gradient and broadening the reflection bandwidth in the sample.