Abstracts

 

Alignment of the Polystyrene-Poly[Methyl Methacralate] Diblock Copolymer
Yitzi Calm (Mark T. Tuominen)

The two copolymers Polystyrene (PS) and Poly[Methyl Methacralate] (PMMA) can be covalently bonded to form the Diblock Copolymer (DBCP). It is well established that the DBCP will undergo self assembly by means of phase separation to form a nanostructured material, and that the resulting structure, which has a length scale on the order of five-forty nm depending on the DBCP's molecular weight, is dependent on the relative proportions of each. Another feature of the DBCP that is observed is that one could bear control over its spatial orientation by means of aligning it with an external electric field. This research focuses ultimately on the simultaneous in plane and out of plane alignment of the lamellar phase of the DBCP. Nanoscale IC's could be made by the use of Nanowire (NW) grids composed of two sets of wires-one made of Au and the other of a semiconducting material; to this effect we attempt to use the aligned lamellar phase of the DBCP to create highly ordered, twenty nm NW grids.

 

Fracture of Polymers and Composites
Jimmy Deng (Allen J. Lesser)

Polymers are commonly used in everyday applications because they are easy to produce and process. One intrinsic property of polymers (i.e., plastics) is that they are generally regarded as tough materials. This implies they have high resistance to fracture. In this project we investigate mechanisms of fracture and tearing in two different types of polymeric materials. The first type consists of tearing thin polypropylene (PP) and polyethylene (PE) films, and the second investigated the fracture of these materials in composite form. Tearing of films showed significant yielding and drawing of material. We used a nonstandard tearing test called the double edged notch test (DENT) to measure the essential work of fracture. This test is done by cutting an edge on either side of a rectangular sheet of our material. The length of the ligament in the middle of the sheet is varied and load versus extension is calculated using an Instron machine. The data is then graphed with the y axis being kilojoules per meters squared and x axis being ligament length in millimeter. Because the scatter was very linear, one can assume that if the line is extrapolated to 0 mm ligament length, we will have the essential work of fracture.

In composite form, the fracture pattern in PP is much more brittle. We are interested in the crack propagation of polypropylene and polyethylene based polymers. Volumetric amounts of 5, 10, 15, and 20% of TBBA (material used in polycarbonate) were mixed samples of polyethylene as well as polypropylene using a single screw extruder. These samples were then processed by a melt press to thicknesses of 1 mm, for tensile tests, and 6 mm, to make samples suitable for viewing under an SEM. Two notches of similar dimension were made on the 6 mm samples so that we could observe crack propagation on a failed portion of the sample as well as one that has not failed yet. After inspection under the SEM, we discovered that the TBBA did not change the mechanical properties of the material. The result was not what we had hoped for so we will repeat the experiment using BPA, a similar compound to TBBA.

 

How Matlab Simulation Data can Predict the Optimum Experimental Route to a Desired Emulsion Drop Distribution
Aimee Khan, (Surita R. Bhatia)

The goal of this project is to use a mathematical model to predict drop diameter distributions coming out of a homogenizer from initial data. A coarse emulsion is made using a shear mixer, and then a fine emulsion is prepared using the homogenizer. The drop distribution is measured using various laser techniques. The pharmaceutical value of emulsions is that it is an economical and safe method for hydrophobic drug delivery via the inner hydrophobic part of the drops. The mathematical model will facilitate scale-up in the pharmaceutical industry since drop distribution is integral to determine correct biodistribution of drugs. The problem is that it is far too expensive and time consuming to carry out all the necessary experiments since there are far too many variables involved in predicting drop distribution. A working mathematical model would be a great advancement in emulsion technology. I investigated the effect of pressure, surface tension, viscosity, initial mean distribution, initial width distribution, and volume fraction on drop size distribution theoretically. From the MATLab program, I gathered mean and variance data. Then I graphed the correlations leaving all values constant each time and changing just one variable. Next they were analyzed and only the most important results were chosen to be presented. General correlations show that increasing pressure in a homogenizer decreases the mean diameter of the drop distribution. Listed from most effective to least effective in increasing drop diameter are surface tension, volume fraction, initial variance, viscosity and initial mean distribution.
 

Heat Denaturation of Model Globular Protein (Beta-lactoglobulin)
Megan E. Murphy (David J. McClements)

The purpose of this study was to develop protein nanoparticles that could be used in a variety of industrial applications. Beta-lactoglobulin was chosen as a model globular protein because it is a common dairy protein whose molecular properties are well understood. Nanoparticle suspensions were prepared by heating 0.5 wt% beta-lactoglobulin solutions at 90 degrees Celsius for 30 minutes at pH values ranging from 3 to 7. The size, charge and stability of the resulting suspensions were measured using light scattering and electrophoresis. Protein nanoparticles with well defined diameters (100nm-500nm) and charges (+50 to -50mV) could be prepared by controlling the molecular interactions between proteins by altering temperature, pH, and ionic strength. Under a narrow range of pH conditions [5.5-6.0] the system was found to form stable nanoparticles with diameter about 200nm. At pH 3 and 7 the solution was transparent, because of large electrostatic repulsion between the protein molecules, and at pH 5.0 a large precipitate was formed because of weak electrostatic repulsion around the protein's isoelectric point. The protein nanoparticles developed in this study may be useful as natural emulsifiers, delivery systems, or fat replacers.
 

Peptide Separation with Amphiphilic Homopolymers
Sean Paradiso (Sankaran Thayumanavan)

There has been much research lately focused on using individual peptides for pharmaceuticals. As a result, there is a need for us to develop ways for researchers to take slurries of cleaved proteins (peptides) and separate them.  Our goal is selective extraction of peptides containing cysteine groups using amphiphilic polymers containing sporadic functionalities with disulfide bonds.  The disulfide bonds, in theory, should cleave upon contact with cysteine, attaching the peptide to the polymer.  Because the polymers that we're experimenting with are amphiphilic, they form these globular inverse micelles (spheres) in apolar solvents.  It has been shown previously that these micelles get kinetically trapped in their solvent of origin (so even after vigorous shaking, the micelles will settle back in the apolar or organic layer).  This means that we should be able to have peptides in aqueous solution below an organic layer containing micellar aggregates of our polymer that get extracted out of the aqueous layer into the organic layer after shaking, able to then be skimmed off the top and analyzed.  This process would lend itself to easy separation.
 

Coating Nanocrystal Quantum Dots With An Amphiphilic Polymer Shell
Thomas Tabb ( Triantafillos J Mountziaris)

Quantum dots (QDs) are semiconductor nanocrystals that exhibit size-dependent luminescence and can be used as luminescent tags for biomolecules. Zinc selenide (ZnSe) QDs synthesized using a hot coordinating solvent technique were coated with an amphiphilic triblock copolymer to allow transfer from an organic to an aqueous solution. In order for ZnSe QDs to be used in biological applications, the particles must be water dispersible. The capping polymer was first prepared by quenching some of its carboxyl groups with octylamine. A cross linker was then added to assist in encapsulation of the QD. Once the polymer was fully primed, it was slowly inserted into the QD/hexane solution. Analysis with fluorescence correlation spectroscopy and dynamic light scattering revealed that the QDs retained their luminescent properties as well their narrow size distribution. Successful solubilization of ZnSe QDs that are able to maintain their high photoluminescence quantum yields is the most difficult step in prepping for biological application. All that is left is to attach a binding molecule to the polymer shell, such as polyethylene glycol (PEG), to allow the QDs to be affixed to biomolecules.
 

Using Amphiphilic Nanocontainers to Separate Compounds by Isoelectric Point
Jacqueline Washington (Richard W. Vachet)

A new class of amphiphilic polymers that self assemble into nanocontainers with charged interiors can selectively extract compounds based on charge. These nanocontainers form inverse micelle-like assemblies that are very useful in the extraction of biological materials, such as peptides. To test the ability of these materials to separate compounds according to isoelectric point (pI), isoelectric focusing markers (IEF markers) will be studied because they have well-defined pI values. pI is the pH at which a molecule has a net charge of zero, and this value is an important physical characteristic of peptides. IEF markers will be very useful for determining the precise extraction selectivity of the nanocontainers. In order to quantitatively measure the amount of IEF marker, a liquid-liquid extraction must be performed at different pH values. The initial hypothesis states: at a pH that is lower than the pI of the IEF marker, the compound is extracted because it is more positively-charged; at a pH that is higher than the marker's pI, the compound is not extracted because it is more negatively-charged and has unfavorable columbic interactions with the interior of the nanocontainer. In conclusion, the data collected partially supports the initial hypothesis. Some of the data does not support the initial hypothesis because the compounds with relatively high pI values were extracted at pH values above their pI values; extraction occurs because the IEF markers are still slightly positive in buffers with high pH values.