Blog #3

Blog #3

 

William Y. Bender

Dr. Krumpfer

March 21, 2017

 

Since the last blog, we have been able to characterize the mechanical (bulk) and surface properties of the newly synthesized materials of crosslinked vinyl-terminated poly(dimethylsiloxane) (v-PDMS) and hydridosiloxanes (Figure 1). The hope is to prepare materials that have antimicrobial properties.  In other words, biofilms will be unable to grow on them.  So far, we have mixed the two polymers in different ratios in order to change the mechanical properties of the silicone materials.  We know from previous work that the mechanical properties have an important role on how cell growth will proceed on the surface. Additionally, we have looked at the effects of different additives on the pdroperties.  For example, we have found that including zinc chloride powder into the material increases the Young’s modulus, and therefore creates materials that are “stiffer”.  This is unsurprising since salts, like zinc chloride, are very hard.  Surprisingly, the addition of titanium dioxide nanoparticles has the opposite effect, and softened the materials.  These effects and be seen by the slope of the line in the stress-strain curves for these materials (Figure 2), where a higher slope means the material is “stiffer.” In contrast to the mechanical properties, the surface properties of these materials show little change with respect to additive, as seen through contact angle analysis.

Figure 1.  Hydrosilyation reaction of vinyl-terminated PDMS and hydridomethylsiloxanes to make robust crosslinked, silicone materials.

Figure 2.  Stress-strain curves for pure silicone (left), zinc chloride-filled silicone (middle), and titanium dioxide filled silicone (right).  Young’s moduli for each of these is 359 mPa, 1,560 mPa, and 234 mPa, respectively.

 

Currently, we have begun preliminary testing of the antimicrobial properties of films of these materials in collaboration with Dr. Andrew Wier’s research group in Biology. Figure 3 shows biofilm growth (stained purple for ease of viewing) on a number of different silicone materials and composites.  While these are purely preliminary and too early to draw real conclusions, there seems to be differences in the amount of biofilm growth on the different samples, which is hopeful for future experiments.

Figure 3.  Biofilm growth on various silicone materials

 

Also during this past semester, I had the opportunity to present what we had been working on at the thirty-sixth annual meeting of the Society of Fellows of Dyson College in March. It was an eye-opening experience, and it exhibited just how much forward-thinking research happens at Pace. Further, I am once again honored to be afforded this research opportunity by the UGR program, considering the quality of the research I saw there.

In summary, we have shown that the mechanical properties of the materials can be altered through the addition of different compounds into the silicone without changing the surface properties.  We plan to continue testing materials, including silicone-organic hybrid materials, and their effects on biofilm growth. We look forward to reporting our results on the next blog!

 

 

Blog 1: “Hard-Soft” Block Copolymers prepared by Hydrosilylation Step-Growth Polymerization

Blog #1

 

William Y. Bender

Dr. Krumpfer

October 17, 2016

Title:    “Hard-Soft” Block Copolymers prepared by Hydrosilylation Step-Growth Polymerization

 

Purpose:

Polymers are linear macromolecules that affect our daily lives in many ways.  Styrofoam and plastic bottles are just some examples of these important materials.  A polymer is prepared from smaller molecules, monomers, which react together to create larger molecules with a repeating structure and properties that can compete against other materials, such as metals, but are much easier and cheaper to prepare.  For these reasons, the ability to prepare new and better polymers is very attractive in many technologies.

In this project, I will be preparing polymers through a step-growth process.  This uses two different monomers that can react with each other over and over again.  One of these monomers will be a siloxane, which are very flexible.  Pure siloxanes are liquids at room temperature and have very high thermal stabilities.  The other monomer will be a carbon-based monomer, which are typically solid at room temperature and have very good mechanical properties.  By combining these two monomers, I hope to prepare polymers that have the high thermal stability of siloxanes and the good mechanical properties of carbon-based polymers without either of their drawbacks.

We can compare these polymers with crosslinked materials.  Adding crosslinks to these polymers will prepare monolithic substances, like rubber.  The mechanical properties can be seen by applying a stress (pressure) on the surfaces and measuring the strain (change in shape). The chemical properties of these materials will be assessed using Infrared Spectroscopy (IR).  Therefore, we can see the effects of chemistry on the mechanical properties of these materials.  By varying the chemistry (types of monomers we use) and number of crosslinks in the material, we expect to be able to control the mechanical properties of the materials we make.

The subject of step growth polymerization is interesting to me as the concepts I have learned so far in organic chemistry are reinforced and enhanced. The types of polymers that can be made are nearly limitless, since there are many different monomers we can use. To begin with, we will primarily be looking at hydridosiloxanes and divinylbenzene reacted using a platinum catalyst in a hydrosilylation reaction.

Blog 2

Blog #2

William Y. Bender

Dr. Krumpfer

December 12, 2016

 

Currently, we have been able to create polymers using hydridosiloxanes (high thermal stability) and divinylbenzene (high mechanical stability) using a platinum based catalyst. As expected, the resulting polymer had a combination of the two monomers characteristic strengths. The mechanical properties of the polymer were seen through the result of a stress and a strain test. By applying weight to the top surface of the polymer we were able to calculate the compressional stress also called normal stress. This is the force perpendicular to the surface of the polymer which acts to compress it. The deformation in the polymer’s height and shape relative to its original quantities is called the strain. The change in height allowed for the calculation of stress: Newtons per square meter (Force per unit area). A plot between stress and strain yielded a linear line indicating that there is a proportionality between the two, following Hooke’s law.

 

Looking forward, we would like to bring this research project more in line with my major, Biochemistry. Working in collaboration with the research group of Dr. Wier in the biology department, we will be analyzing the growth of biofilm forming bacteria on these  hydridosiloxane-divinylbenzene polymers with varying amounts of zinc ions (Zn2+) suspended in the crosslinked polymer. Studies have backed up the effectiveness of zinc oxides antimicrobial properties on the surface of titanium implants used in dental system applications. The formation of zinc oxide on the surface of polymers can extend the usefulness of surface embedded zinc due to polymers being used in many more applications.