Ji Won Hwang

Fast dynamics and relaxation of colloidal drops during the drying process using multispeckle diffusing wave spectroscopy.

The fast dynamics generated by the Brownian motion of particles in colloidal drops, and the related relaxation during drying, which play key roles in suspension systems, were investigated incorporating multispeckle diffusing wave spectroscopy (MSDWS). MSDWS equipment was implemented to analyze the relaxation properties of suspensions under a nonergodic and nonstationary drying process, which cannot be elucidated by conventional light scattering methods, such as dynamic light scattering and diffusing wave spectroscopy. Rapid particle movement can be identified by the characteristic relaxation time, which is closely related to the Brownian motion due to thermal fluctuations of the particles. In the compacting stage of the drying process, the characteristic relaxation time increased gradually with the drying time because the particles in the colloidal drop were constrained by themselves. Moreover, variations of the initial concentration and particle size considerably affected the complete drying time and characteristic relaxation time, producing a shorter relaxation time for a low concentrated suspension with small particles.

Rheology and curing characteristics of dual-curable clearcoats with hydroxyl functionalized urethane methacrylate oligomer: Effect of blocked isocyanate thermal crosslinkers

Rheological and mechanical properties of dual-curable automotive clearcoats containing different blocked isocyanate thermal crosslinkers (HDI, IPDI, and SMBI) have been compared by changing dual-curing sequences, i.e., UV-thermal dual curing and thermal-UV dual curing. Real-time elastic modulus data of clearcoats measured during several curing procedures have been correlated with the formation of crosslinked networks inside clearcoats. Clearcoat with SMBI shows increased modulus data due to the more reactive nature of functional groups in SMBI. Difference of rheological data of clearcoats under different curing temperatures during dual-curing sequences has been interpreted with the transition of chemical reactions inside clearcoats with different chemical structured crosslinkers. It turns out that scratch properties of cured clearcoats are also affected by the dual-curing sequence.

Expression of SOCS1 and SOCS3 is altered in the nasal mucosa of patients with mild and moderate/severe persistent allergic rhinitis.

Background: The aim of this study was to evaluate the role of suppressor of cytokine signaling (SOCS) molecules, SOCS1 and SOCS3, which act as negative regulators of cytokine signaling in various allergic diseases, in patients with mild and moderate/severe persistent allergic rhinitis. Methods: The expression and distribution pattern of SOCS1 and SOCS3 were analyzed in nasal mucosa and peripheral blood mononuclear cells (PBMC) of healthy controls, and patients with mild and moderate/severe persistent allergic rhinitis using RT-PCR, immunohistochemistry and Western blotting. IL-4, IL-13, IL-15 and IFN-γ expression was also analyzed in the nasal mucosa of each individual using RT-PCR and Western blotting. Results: SOCS1 and SOCS3 mRNA and protein expression was significantly increased in the nasal mucosa and PBMC of patients with mild and moderate/severe persistent allergic rhinitis compared with healthy controls. In healthy and allergic nasal mucosa, they were commonly localized to the epithelium, submucosal glands and endothelium, showing stronger staining intensity in mild and moderate/severe persistent allergic nasal mucosa than in healthy nasal mucosa. Tissue levels of IL-4 and IL-13 were increased in moderate/severe persistent allergic nasal mucosa whereas IL-15 and IFN-γ were decreased in moderate/severe persistent allergic nasal mucosa. Conclusions: Upregulation of SOCS1 and SOCS3 in mild and moderate/severe persistent allergic rhinitis suggests that SOCS proteins may be important regulators in the pathogenesis of allergic rhinitis and play a role as molecular determinants of allergic rhinitis persistence.

The effect of thermal radical initiator derived from O-imino-isourea on thermal curing characteristics and properties of automotive clearcoats

Curing characteristics of melamine-based automotive clearcoats with or without thermal radical initiator (TRI) derived from an O-imino-isourea have been examined by means of their real-time rheological properties during a thermal curing process. By changing functionalities of reactive sites at hydroxyl groups and unsaturated double bonds in hydroxyl-functionalized urethane methacrylate oligomer as a main binder, the effect of TRI on various properties of thermally cured clearcoats has been compared by means of rheological, rigid-body pendulum, ultra nano-indentation, and nano-scratch tests. It was found that a small portion of TRI significantly enhanced the final elastic modulus of clearcoats with the lower content of hydroxyl groups and considerably shortened curing time, implying the formation of denser crosslinked networks inside clearcoats by the free-radical polymerization at relatively lower curing temperature. These results were directly linked with the improvement of their mechanical properties such as indentation hardness and scratch resistance. TRI plays a key role in desirably controlling the rheological and mechanical properties of clearcoats under insufficient thermal curing conditions.