Effects of changing solvent on monolayer formation

Three different samples were made using two different ratios of ethanol as solvent.  Two samples were made using a 1:1 ratio of water/ethanol and the 100 nm sphere diffusion, the first being the normal 1 cm squared and the other being about .25 cm squared.  The second was to make sure that the movement of the barrier which increase the concentration of spheres near the surface of the sample was not effecting the film formation.  The third sample was done with 200 spheres and pure ethanol as the solvent.  The first two samples showed the same coverage compared to each other but greater than when methanol was used.  The third sample showed very good coverage, but drops of liquid formed and remained in place until the drops were farther away from the liquid-air interface and then slid down the surface of the sample. creating chaotic multilayers in the areas where the drop slid.  The other areas shows little to no streakiness with the naked eye.  The only problem I can find with using methanol and ethanol as a solvent is that they evaporate from the solution very quickly, reducing the volume of the solution in the trough.  Also, because the SDS is decreasing only when dipping is performed and the solvent is evaporating much faster than the SDS is leaving, I believe the SDS concentration is increasing over time.  The SDS is used as a spreading agent and the optimal concentration has been found around 34.7 mM (1).  As the concentration increases above this the spheres begin to form multilayers or clusters of spheres.
This increase in SDS concentration will not occur appreciably over the course of dipping in the trough but over the course of a few days and with the use of sonication the amount may become enough to cause a difference in monolayer formation.  That said, results show that a ratio in begin 100% ethanol and a 1:1 water/ethanol mixture may give the best results we can hope for without further study in the formation of monlayers of Poly-styrene microbeads on silica.  Will proceed from here and make as many samples in as short amount of time as possible to try and counteract the evaporation of ethanol from solution and move.  On a personal not, I've learned over the past few weeks that try as you might to make every little part of the project go perfectly, it probably won't.  However, I have learned new concepts through trying to perfect the films for my samples and can apply them later or come back and try again if they still are not sufficient.  For now, they will work for what we are trying to investigate and that is what is important.  Don't lose the forest for the trees.

Monolayers update

A variety of silica samples were made using the modified Langmuir-Blodgett dipping method (1), varying the conditions  for each and SEM was performed.  A long range hexagonal monolayer was not formed but a few displayed streaks of monolayer spheres.  Spin coating was also performed however this also failed to create even streaky monolayer coverage of the sample.  One more method will be attempted before moving on to the next stage and working with the streaky monolayers and that is using ethanol as the solvent as well as increasing the immersion time before withdrawing the sample from the Langmuir trough.  The amount of coverage of the monolayers is not as crucial to this project as having some coverage.  The next phase is to create nanopillars on the surface, which will occur in the areas with nanosphers.  

(1) 

The Use of Surface Tension to Predict the Formation of 2D Arrays of Latex Spheres Formed via the Langmuir−Blodgett-Like Technique

Maricel Marquez and and Brian P. Grady*

Langmuir 2004 20 (25), 10998-11004

Update of monolayer formation attempts

SEM images have been taken of the previous samples and have shown that monolayers were indeed formed but not nearly close enough to the surface areas that we are looking for.  After doing some reading there are methods done using a spin coater that are worth looking into trying.  I have also contacted the previous operator of the Langmuir-Blodgett trough being used and she has given me a few tips which may also prove fruitful.  Over the next week I hope to try and employ both methods and next Friday possibly take SEM images to check for whether or not one of the techniques works for our project.