Molecular dynamics study of the role of the free surface on block copolymer thin film morphology and alignment.

Next-generation applications of block copolymer thin films will require a better understanding of the driving forces unique to thin film coatings, specifically those arising from the polymer-air interface. Previous modeling studies of film morphology have treated rigidly confined films, neglecting free surface considerations altogether. We report in this article the first systematic molecular dynamics investigation of block copolymer thin film ordering for unconfined films. We investigate the molecular basis of the formation of a number of experimentally relevant coating features, including surface islands and vertical lamellae. Surface islands are found to form in response to film incommensurability, whereas commensurability considerations are insufficient to explain vertical lamellar formation. Dynamics of lamellar formation presented herein demonstrate that vertical lamellar orientation is initiated in the surface regions of the film, most strikingly at the free surface. We conclude that the free surface plays a pivotal role in the free energy balance determining overall film morphology, and that confinement models provide an incomplete explanation of the physical basis of morphology selection in block copolymer coatings.

Effect of castration on male rabbit lower urinary tract tissue enzymes.

OBJECTIVES: The influence of testosterone on the prostate and corpus cavernosum have been studied extensively. However, the influence of testosterone on the lower urinary tract (bladder and urethra) have not been investigated to any great extent. The aim of this study was to determine whether androgen deprivation alters lower urinary tract metabolism. METHODS: A total of 16 rabbits were divided into four groups of four rabbits each. Each rabbit in groups 1-3 underwent surgical bilateral castration for duration of 1, 2 , and 4 weeks, and group 4 underwent sham operations. Sections of bladder body and base wall and mucosa, urethra and corpora were isolated, frozen, and stored under liquid nitrogen. The activities of citrate synthase-thapsigargin sensitive Ca(2+) ATPase (Sarco/Endoplasmic Reticulum Ca(2+ )ATPase [SERCA]), and choline acetyl-transferase were examined as markers for mitochondrial function, sarcoplasmic reticular calcium storage and release, and cholinergic nerve function, respectively. RESULTS: The activity of SR function indicator, Ca(2+) ATPase was significantly higher in the control corpora than in the control bladder or urethra. Castration resulted in decreased activity in the mitochondria specific enzyme, citrate synthase, the activity of which was greatest in the urethra and lowest in the corpora. Cholinergic nerve density indicator, choline acetyl-transferase activity was greatest in the bladder body and lowest in the urethra. CONCLUSIONS: Our data indicate that (1) significant differences exist in the activities of all three enzymes in the various organs associated with the lower urinary tract; and (2) that castration results in significant alterations in the activities of all three enzymes in the bladder body, base, urethra, and corpora.