It is increasingly difficult to keep up with the blog. We are learning and doing at a rapid pace. We are glad there are three of us, as each one feels no single soul could receive, process, annotate, and use this information without someone else to fill in the inevitable blank spaces.
Chelsea fields a question concerning adhesion and adnhesion force...exactly what are those? Adhesion is measured using separation force which is measured in millinewtons through a process called "contact adhesion testing". One surface is glass of well defined properties and geometry. Bring it and another surface together at a known rate with a known force and press to a given compressive force which you determine, then pull them apart (separate them) at a given rate, get a tensile force as you separate the two, the maximum tensile force is separation force, which occurs at the point/moment of separation.
We use the inverted microscope to complete the images from Jennifer's PDMS sample made from Doug's mold. Chelsea then showed us how to use Image J for data analysis. This program can be downloaded free (google it). We need to store the information on the UMass network so all four of us (Chelsea too!) can access it. It is important to remember to open Image J and import the photographs you wish to analyze and any calibration photographs first. The next step is to set the calibration; after drawing
Friday, July 11, 2008
Tuesday, July 8, 2008
Wednesday July 2, 2008 PDMS, UVO and Contact Angle
Using the 10:1 pre-polymer/curing agent ratio, we prepared several vials of PDMS and poured them into the glass slide molds Chelsea has; we made slabs of PDMS. We cured the PDMS for 20 minutes in the 110C oven, then cut around the edges of the mold with a razor blade to de-mold the solid PDMS slab. The "good" side of the slab is the side that was down inside the mold (uh-oh!), because the top as it sits in the mold will have a meniscus (bad). So, for future reference, it is important to place the de-molded slab down-side facing up on the glass slide. The slab is stored in a Petri dish to minimize dust and dirt. We then expose these slabs to UVO cleaning. The UVO cleaner has its on/off switch on a power strip to the left of the instrument. It needs to be turned on 5 minutes prior to use to get to temperature. The UVO cleaner exposes the samples to free oxygen radicals and UV light; this causes oxygen to replace the methyl groups on the polydimethylsiloxane (PDMS), making the surface more hydrophilic. Eventually, an H attaches to the O making an OH group. We expose samples for 5, 10, 20 and 30 minutes.
After this has been accomplished, we use the Zeiss inverted microscope to examine Jennifer's PDMS sample, made from Doug's mold, and take pictures of the hex holes to use in calculating the volume of the wells. We waste an amazing amount of time trying to draw the hex array to label which holes we are measuring; Chelsea is amused by this as this step is totally unnecessary. I have a gorgeous useless drawing of a hex array in my lab notebook now though. We develop a system for labeling the hex arrays and we photograph three circles from each hex on the PDMS sample. The hex with the smallest holes is in the upper left corner, and that is array A1 and we sample 3 holes in that array: a, b, and c. The horizontal rows of hexes have numbers, and the vertical columns of hexes have capital letter designations. We can now easily locate the hex for each photograph. The images we take are saved in the Users folder, RET subfolder in the desktop.
In the afternoon we go to the Carter lab on the fourth floor and learn how to use the contact angle measuring device, the VCA Optima made by AST products, pictured above. The procedure for using this instrument may be found on the side margin of this blog. The contact angle measurement gives us a quantified measurement of the hydrophobic/hydrophilic nature of material. We are testing the static contact angle today to quantify the effect of UVO exposure of PDMS. We observe a relationship between UVO exposure and contact angle measurements: the greater the UVO exposure, the more hydrophilic the PDMS surface (makes sense. more O present on PDMS surface) and the lower the contact angle. We need to test more samples with different amounts of UVO exposure so that we can construct a graph of our results. Samples tested today are 0 , 5,10,20, and 30 minutes of UVO exposure. We will make samples with 45, 60, 75, and 90 minutes of UVO exposure next week to test.
Monday, July 7, 2008
Tuesday July 1, 2008
We made PDMS as soon as we arrived. Sadly, I goofed up ad put the incorrect pre-polymer in the dispensing bottle. Not a tragedy, but not correct. We obtained a new dispensing bottle and filled it with the Sylgard 184 pre-polymer that we should be using. We mix up the PDMS in a 1:10 ratio, degas it, then fill ring molds made by masking silicon wafers. We cure the PDMS for 30 minutes in the 110 C oven, coll and de-mold them. We will take pictures of the molds using the Zeiss Axiovert 300M microscope (Scope 1), then analyze the pictures using Image J to determine the diameter of the wells in the PDMS (left by the posts on the molds). We will also use Image J to determine the distance between the wells. The profilometer will be used to determine the depth of the wells. From this data, we will create an Excel sheet to calculate the volume of the wells. This will allow us to characterize the molds we are working with.
After making our PDMS molds of hexagonal arrays of wells, Chelsea teaches us to use the Zeiss Axiovert 300 m. Refer to the procedure on the side of this blog.
We made PDMS as soon as we arrived. Sadly, I goofed up ad put the incorrect pre-polymer in the dispensing bottle. Not a tragedy, but not correct. We obtained a new dispensing bottle and filled it with the Sylgard 184 pre-polymer that we should be using. We mix up the PDMS in a 1:10 ratio, degas it, then fill ring molds made by masking silicon wafers. We cure the PDMS for 30 minutes in the 110 C oven, coll and de-mold them. We will take pictures of the molds using the Zeiss Axiovert 300M microscope (Scope 1), then analyze the pictures using Image J to determine the diameter of the wells in the PDMS (left by the posts on the molds). We will also use Image J to determine the distance between the wells. The profilometer will be used to determine the depth of the wells. From this data, we will create an Excel sheet to calculate the volume of the wells. This will allow us to characterize the molds we are working with.
After making our PDMS molds of hexagonal arrays of wells, Chelsea teaches us to use the Zeiss Axiovert 300 m. Refer to the procedure on the side of this blog.
Wednesday, July 2, 2008
Monday June 30, 2008 : Making PDMS
Jennifer, Jennifer and I start out the day with Chelsea Davis and Doug Farmer, who outline our program. Yuri will also be working with us. Doug is a fourth year, Chelsea is a second year, and Yuri is a first year PhD student.
PDMS is made of a pre-polymer (Dow Corning Sylgard 184) and a cross linking (curing) agent. We will be using a 10:1 ratio; ten parts of pre-polymer and one part cross linking agent. We make a 10:1 and a 20:1 sample of PDMS just to see the difference between the two. The 10:1 is much less flexible than the 20:1. This makes sense because there is less cross linker per ml in the 20:1 than in the 10:1, so the 10:1 should be stiffer.
When making PDMS, it is important that time is allowed for bubbles trapped during the mixing process to rise to the surface and be released. This can be done by either using a desicator with a vacuum pump attached (this can be a bit dangerous as too much vacuum applied too fast causes the PDMS to overflow its container), or by letting the PDMS sit for a while (an hour or so) then blowing the bubbles off of the surface. The PDMS is cured into the desired mold, and cured to hardness in one of three ways. The PDMS can sit a room temperature for 24 hrs, or it can cure in a 70 C oven for 3 hours, or it can cure in the 110 C oven for 20 minutes. Each process results in a slightly different stiffness of the product (heat increases the chance of the cross linker coming in contact with the pre-polymer). Once the PDMS has cured, remove it from the mold using a razor blade: the deisred side of the PDMS is DOWN inside the mold, not the top surface. The top surface will have a meniscus, while the bottom surface will be shaped by the mold. The removed, molded PDMS should be placed on a glass slide; the side of the PDMS that was down in the mold is now up on the glass slide. Store the PDMS in a petri dish until you are ready to use it. It will be useful for about 6 hrs.
We were given three papers to read, one concerning how PDMS cross links and how exposure of PDMS to UVO (Ultaviolet light and ozone) creates a glassy surface on the PDMS. This occurs because the methyl groups, normally found attached to the Si as a side branch in the Si-O-Si-O chain is replaced by oxygen, which then becomes a hydroxyl group. This makes the surface similar to SiO2, or glass. This new surface is hydrophilic (oxygen present) whereas the CH3 was hydrophobic. This changes the properties of the PDMS in other ways as well, affecting elasticity.
The UVO oven needs to be turned on about five minutes prior to use. Place the sample, on a glass slide, in the oven, then close the drawer tightly. Set the timer for the desired exposure, then watch to see if the blue light comes in in the top center of the drawer. If it is on, the UVO exposure is underway. The oven will shut itself off with the timer expiration.
In the afternoon, we learn how to use the VEECO DEKTAK 150 PROFILOMETER. It is mounted on a vibration free table, as the instrument is sensitive to vibration and this could substantially affect results. The instrument is quite sensitive; the tip used to measure depth/thickness has a 12.5 micron radius. The stage of the instrument is motorized for optimum control and to prevent damage to the instrument.
SEE PROFILOMETER Dektak 150 PROCEDURE For Operating Instructions.
In the afternoon, Doug taught us about contact angle and how it can be used to measure surface energy. Hydrophilic materials have low surface energy and a low contact angle. Hydrophobic materials have high surface energy and higher contact angles.
Jennifer, Jennifer and I start out the day with Chelsea Davis and Doug Farmer, who outline our program. Yuri will also be working with us. Doug is a fourth year, Chelsea is a second year, and Yuri is a first year PhD student.
PDMS is made of a pre-polymer (Dow Corning Sylgard 184) and a cross linking (curing) agent. We will be using a 10:1 ratio; ten parts of pre-polymer and one part cross linking agent. We make a 10:1 and a 20:1 sample of PDMS just to see the difference between the two. The 10:1 is much less flexible than the 20:1. This makes sense because there is less cross linker per ml in the 20:1 than in the 10:1, so the 10:1 should be stiffer.
When making PDMS, it is important that time is allowed for bubbles trapped during the mixing process to rise to the surface and be released. This can be done by either using a desicator with a vacuum pump attached (this can be a bit dangerous as too much vacuum applied too fast causes the PDMS to overflow its container), or by letting the PDMS sit for a while (an hour or so) then blowing the bubbles off of the surface. The PDMS is cured into the desired mold, and cured to hardness in one of three ways. The PDMS can sit a room temperature for 24 hrs, or it can cure in a 70 C oven for 3 hours, or it can cure in the 110 C oven for 20 minutes. Each process results in a slightly different stiffness of the product (heat increases the chance of the cross linker coming in contact with the pre-polymer). Once the PDMS has cured, remove it from the mold using a razor blade: the deisred side of the PDMS is DOWN inside the mold, not the top surface. The top surface will have a meniscus, while the bottom surface will be shaped by the mold. The removed, molded PDMS should be placed on a glass slide; the side of the PDMS that was down in the mold is now up on the glass slide. Store the PDMS in a petri dish until you are ready to use it. It will be useful for about 6 hrs.
We were given three papers to read, one concerning how PDMS cross links and how exposure of PDMS to UVO (Ultaviolet light and ozone) creates a glassy surface on the PDMS. This occurs because the methyl groups, normally found attached to the Si as a side branch in the Si-O-Si-O chain is replaced by oxygen, which then becomes a hydroxyl group. This makes the surface similar to SiO2, or glass. This new surface is hydrophilic (oxygen present) whereas the CH3 was hydrophobic. This changes the properties of the PDMS in other ways as well, affecting elasticity.
The UVO oven needs to be turned on about five minutes prior to use. Place the sample, on a glass slide, in the oven, then close the drawer tightly. Set the timer for the desired exposure, then watch to see if the blue light comes in in the top center of the drawer. If it is on, the UVO exposure is underway. The oven will shut itself off with the timer expiration.
In the afternoon, we learn how to use the VEECO DEKTAK 150 PROFILOMETER. It is mounted on a vibration free table, as the instrument is sensitive to vibration and this could substantially affect results. The instrument is quite sensitive; the tip used to measure depth/thickness has a 12.5 micron radius. The stage of the instrument is motorized for optimum control and to prevent damage to the instrument.
SEE PROFILOMETER Dektak 150 PROCEDURE For Operating Instructions.
In the afternoon, Doug taught us about contact angle and how it can be used to measure surface energy. Hydrophilic materials have low surface energy and a low contact angle. Hydrophobic materials have high surface energy and higher contact angles.
Friday June 27, 2008
Today, former R.E.T.s, including me, gave presentations of their experiences in past R.E.T. programs. I gave two presentations; one on wrinkling discussing my research from last summer, and the second on the program Professor Crosby, Dr. Dabkowski, and I developed for the seven Minnechaug students that we piloted last year. The main focus of my experience here this summer will be to develop a protocol for this program so that toher schools might participate. The seminars took most of the day. It was great to reconnect with people from last summer and also to see Cathy Levesque, a former HWRSD teacher. She was given an award by MRSEC for her work furthering science education. She is currently the K-12 science coordinator for Westfield Public Schools.
Today, former R.E.T.s, including me, gave presentations of their experiences in past R.E.T. programs. I gave two presentations; one on wrinkling discussing my research from last summer, and the second on the program Professor Crosby, Dr. Dabkowski, and I developed for the seven Minnechaug students that we piloted last year. The main focus of my experience here this summer will be to develop a protocol for this program so that toher schools might participate. The seminars took most of the day. It was great to reconnect with people from last summer and also to see Cathy Levesque, a former HWRSD teacher. She was given an award by MRSEC for her work furthering science education. She is currently the K-12 science coordinator for Westfield Public Schools.
Thursday, June 26, 2008
Thursday June 26 2008
This morning Greg did his polymer "Road Show". I have seen it four times now, but I still get something new out of it each time. The Elmer's Glue/borax mix to create "slime" is a great experiment to show what cross linking is in polymers, but today I realized I could use it to show the difference between starch (no side chains) and cellulose (side chains). I plan on using it in Sept.
Al Crosby came to lunch with us to discuss our expectations for the experience. The two
Jennifers will focus on crumpling; I will do some work with them but will focus on writing the curriculum and the expectations for the High School Research Experience program we piloted this year. Doug Farmer, Chelsea Davis and Yuri will be working with us. C.J. should finish his dissertation and have his defense before we leave. I would like to attend.
Al was appointed full professor this week...so richly deserved in my opinion. Just wonderful. He will be away for a week while we all get started.
This morning Greg did his polymer "Road Show". I have seen it four times now, but I still get something new out of it each time. The Elmer's Glue/borax mix to create "slime" is a great experiment to show what cross linking is in polymers, but today I realized I could use it to show the difference between starch (no side chains) and cellulose (side chains). I plan on using it in Sept.
Al Crosby came to lunch with us to discuss our expectations for the experience. The two
Jennifers will focus on crumpling; I will do some work with them but will focus on writing the curriculum and the expectations for the High School Research Experience program we piloted this year. Doug Farmer, Chelsea Davis and Yuri will be working with us. C.J. should finish his dissertation and have his defense before we leave. I would like to attend.
Al was appointed full professor this week...so richly deserved in my opinion. Just wonderful. He will be away for a week while we all get started.
Wednesday, June 25, 2008
First Day, June 25, 2005
I am so excited to be back! There are nine others, some local (Westfield, West Springfield, and Belchertown), some from the Boston area, and two from New Hampshire. The farthest traveler is from Florida. I am a little nervous about making my presentation on Friday, but as GReg said, I know more than any of them do, so it should be just fine. I want to be sure to blog the experience again this year as it was so helpful last year. I dont know if I remember how to do all the fanch things Efron taught me though!
Subscribe to:
Comments (Atom)
