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Retention of students to science, technology, engineering, and mathematics (STEM) major has been studied for four cohorts participating in a summer bridge program supported by the National Science Foundation. Students participated in a 6-week program prior to their first term of enrollment at a research-intensive land grant university. Comparisons to baseline incoming classes from 2009-2011 show gains in retention to major out to the third year for underrepresented minorities (African American, Hispanic, Native American), first-generation college students, and females. Gains for underrepresented minorities and females are statistically significant, whereas those for first-generation students are not. These gains are associated with participation in a 6-week summer bridge program and the resulting improvement in preparation for college coursework, sense of belonging as measured by qualitative surveys, and use of academic support structures.

A micromanufacturing lab-on-a-chip project with a nanotechnology component was introduced as an alternate laboratory in the required first-year engineering curriculum at The Ohio State University. Nanotechnology is introduced in related reading and laboratory tours as well as laboratory activities including a quarter-length design, build, and test problem using project management skills found in the standard lab sections. Comparison between pilot and non-pilot students showed no difference in performance on examination questions regarding fundamentals of engineering. (Contains 3 tables and 5 figures.)

A poly(methyl methacrylate) (PMMA) and nanoclay composite was dispersed into polystyrene (PS) using a twin-screw extruder. The mixture was then batch foamed with supercritical C[O.sub.2]. It was found that the cell density of foams based on the blend is higher than that based on the weight average of the two pure polymer components at the same foaming conditions. The cell size decreases and the cell density increases with the increase of the PMMA domain size. One explanation is that the large PMMA domains serve as a C[O.sub.2] reservoir and the nucleation in the PS phase is enhanced by the diffusion of C[O.sub.2] from the PMMA phase to the PS phase. Very small PMMA domains cannot function as a C[O.sub.2] reservoir, and so they are not able to facilitate the nucleation. A much higher cell density and smaller cell size were observed when nanoclay was located at the interface of the PMMA and the PS domains, serving as the heterogeneous nucleating agents. POLYM. ENG. SCI., 47:103-111, 2007. © 2007 Society of Plastics Engineers, INTRODUCTION Typical physical foaming agents [1-4] are volatile chemicals, such as chlorofluorocarbons (CFC), volatile hydrocarbons and alcohols, or inert gases (nitrogen, carbon dioxide, argon, and water). The traditional CFC physical [...]

Intercalated and exfoliated polystyrene/nano-clay composites were prepared by mechanical blending and in situ polymerization respectively. The composites were then foamed by using [CO.sub.2] as the foaming agent in an extrusion [...]

The continuous production of polystyrene microcellular foams with supercritical 002 was achieved on a two-stage single-screw extruder. Simulations related to the foaming process were accomplished by modeling the phase equilibria with the Sanchez-Lacombe equation of state and combining the equations of motion, the energy balance, and the Carreau viscosity model to characterize the flow field and pressure distribution in the die. The position of nucleation in the die was determined from the simulation results via a computational fluid dynamics code (FLUENT). Experimental parameters were selected according to the [T.sub.g] and phase equilibria. The effects of [CO.sub.2] concentration and die pressure are explored. Below the solubility limit, higher [CO.sub.2] concentrations lead to smaller cell size and greater cell density. With an increase of die pressure, the cell size decreases and the cell density increases., INTRODUCTION Art and Science of Microcellular Foaming Polymers Foamed polymers are found in applications ranging from insulation to adsorbents (1). Depending on the application, various foam structures are produced by [...]

Supercritical carbon dioxide (sc[CO.sub.2]) was added during blending of polystyrene or poly(methy1-methacrylate) (PMMA) and a rubber impact modifier (SP 2207). The resulting blend morphologies were compared. The compounding took place in a Leistritz ZSE-27 twin-screw extruder at 100 RPM, at a temperature of 200°C, and with 2.0 wt% [CO.sub.2] injection. The viscosity reduction of PMMA, polystyrene, and SP 2207 was measured using a slit die rheometer attached to the twin-screw extruder. A viscosity reduction of up to 84% was seen with PMMA, 70% with polystyrene and 30% with SP 2207. The solubility of [CO.sub.2] in these polymers was measured in a high-pressure vessel at 200°C and 13.78 MPa (2000 psi). A solubility of 5.79 wt% [CO.sub.2] was seen with PMMA, 3.65 wt% with polystyrene, and 2.60 wt% with SP 2207. The injection of [CO.sub.2] reduced the size of the dispersed rubber phase in both polystyrene and PMMA. For both blends (polystyrene/SP 2207 and PMMA/SP 2207) with and without the injecti on of [CO.sub.2], the extruder length for phase inversion was shortened by about L/D = 4, or 10% of the total extruder length. The impact strength for a 70/30 polystyrene/SP 2207 blend was increased by 26% by the addition of [CO.sub.2]. The improvement in impact strength was not as large for blends of PMMA and SP 2207., L. James Lee (*) David L. Tomasko (*) INTRODUCTION Blending offers polymer processors the most efficient way to satisfy new requirements for material properties. Mixing that occurs in continuous mixers [...]

We have used polymer density functional theory to analyze the equilibrium density profiles and interfacial properties of thin films of polymer in the presence of CO2. Surface tension, surface excess adsorption of CO2 on polymer surface, and width of the interface are discussed. We have shown the changes in these properties in the presence of CO2 and with increasing film thickness and their inverse linear relationship with increasing chain length. One of our important findings is the evidence of segregation of end segments toward the interface. We have introduced a new method of representing this phenomenon by means of Δ profiles that show increase in segregation owing to the presence of CO2 and with increasing chain length. We also make predictions for the octacosane-CO2 binary system near the critical point of CO2. Our results indicate qualitative trends that are comparable to the similar experimental and simulation studies. [ABSTRACT FROM AUTHOR]

L. JAMES LEE [*] DAVID L. TOMASKO [*] Supercritical carbon dioxide ([scCO.sub.2]) was added during compounding of polystyrene and poly(methyl methacrylate) (PMMA) and the resulting morphology development was observed. The [...]

A method for blending polystyrene and poly(methyl methacrylate), (PMMA), with the addition of supercritical carbon dioxide has been investigated. The first series of blends was a PMMA and polystyrene with similar melt viscosities. The second series of blends was a PMMA and polystyrene with a viscosity ratio ([Eta]PMMA/[Eta]polystyrene) of about 20. The results show that a reduction in the size of the minor or dispersed phase is achieved when supercritical carbon dioxide is added to the blend system. A high-pressure mixing vessel was used to prepare the blends under pressure with carbon dioxide for batch blending. The solubilities of C[O.sub.2] in PMMA and polystyrene, measured in the high-pressure mixing vessel at 200 ° C and 13.78 MPa (2000 psi) was 5.8 and 3.6 wt%, respectively. A single screw extruder was used to study the effects of carbon dioxide on the viscosity of polymer melts. The melt viscosity of PMMA was reduced by up to 70% with approximately 0.4 wt% C[O.sub.2]. The melt viscosity of polystyrene was reduced by up to 56% with a C[O.sub.2] content of 0.3 wt%. A twin screw extruder was used to study the effects of injecting carbon dioxide in a continuous compounding operation., INTRODUCTION The blending of immiscible polymers offers processors the opportunity to create materials with a wide range of properties that include improved processing and end use capabilities. The great majority [...]

Electrospinning is one of the efficient processes to fabricate polymeric fibrous scaffolds for several biomedical applications. Several studies have published to demonstrate drug release from electrospun scaffolds. Blends of natural and synthetic electrospun fibers provide excellent platform to combine mechanical and bioactive properties. Drug release from polymer blends is a complex process. Drug release from polymer can be dominated by one or more of following mechanisms: polymer erosion, relaxation, and degradation. In this study, electrospun polycaprolactone (PCL)–gelatin blends are investigated to understand release mechanism of Rhodamine B dye. Also, this article summarizes the effect of high-pressure carbon dioxide on drug loading and release from PCL–gelatin fibers. Results indicate that release media diffusion is a dominant mechanism for PCL–gelatin electrospun fibers. Thickness of electrospun mat becomes critical for blends with gelatin. As gelatin is highly soluble in water and has tendency of gelation, it affects diffusion of release media in and out of scaffold. This article is a key step forward in understanding release from electrospun blends. [ABSTRACT FROM AUTHOR]

This study investigated the effects of hydrophobic-hydrophilic interactions on dual drug release from CO2-infused nanofibers scaffolds (PCL, PCL-gelatin, and PCL "core" PCL-gelatin "shell") using BODIPY 493/503 and Rhodamine B fluorescent dyes as drug models. Favorable dye-scaffold interactions increased total dye loading and promoted steady, more linear release. Unfavorable dye-scaffold interactions reduced overall loading and led to a greater burst release of dye. However, when CO2 was used to infuse dye into an unfavorable scaffold, the changes in loading and release were less pronounced. When two dyes were infused, these behaviors were accentuated due to interactions between the dissolved forms of the dyes. Core-shell composite nanofibers displayed radically different release properties versus pure PCL-gelatin fibers when treated with dyes via CO2 infusion. Dye release from core-shell scaffolds was highly sensitive to both interactions with scaffolds and the phase of CO2 used to infuse the compounds of interest. By using different phases of CO2 to partition dyes into hydrophobic and hydrophilic sections of core-shell nanofibers, such interactions can be manipulated to develop a bimodal drug release system with potential application in drug delivery or tissue engineering. [ABSTRACT FROM AUTHOR]