New User Special Price Expires in

Let's log you in.

Sign in with Facebook


Don't have a StudySoup account? Create one here!


Create a StudySoup account

Be part of our community, it's free to join!

Sign up with Facebook


Create your account
By creating an account you agree to StudySoup's terms and conditions and privacy policy

Already have a StudySoup account? Login here


by: Ms. Schuyler Kozey
Ms. Schuyler Kozey
GPA 3.78


Almost Ready


These notes were just uploaded, and will be ready to view shortly.

Purchase these notes here, or revisit this page.

Either way, we'll remind you when they're ready :)

Preview These Notes for FREE

Get a free preview of these Notes, just enter your email below.

Unlock Preview
Unlock Preview

Preview these materials now for free

Why put in your email? Get access to more of this material and other relevant free materials for your school

View Preview

About this Document

Class Notes
25 ?




Popular in Course

Popular in Physics 2

This 3 page Class Notes was uploaded by Ms. Schuyler Kozey on Monday September 7, 2015. The Class Notes belongs to PHYS 105 at University of California - Santa Cruz taught by Staff in Fall. Since its upload, it has received 23 views. For similar materials see /class/182314/phys-105-university-of-california-santa-cruz in Physics 2 at University of California - Santa Cruz.


Reviews for Mechanics


Report this Material


What is Karma?


Karma is the currency of StudySoup.

You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!

Date Created: 09/07/15
VOLUME 80 NUMBER 15 PHYSICAL REVIEW LETTERS 13 APRIL 1998 ReactionInduced Phase Separation Dynamics A Polymer in a Liquid Crystal Solvent J B Nephew T C Nihei and S A Carter Physics Department University of California Santa Cruz California 95064 Received 8 September 1997 The dynamics of addition polymerizationinduced phase separation in a liquid crystal solvent is examined via confocal microscopy in systems where the nal morphology consists of nematic liquid crystal domains suspended in a crosslinked polymer matrix For low polymer concentrations we observe unusually rapid hydrodynamics and coalescence during phase separation that determine the nal composite morphology This hypercoalescence can result from polymerizationinduced changes of the solubility of the polymer matrix in the liquid crystal solvent PACS numbers 61307v 6141e 6475g Phase separation dynamics of a mixture thermally quenched from a stable to unstable regime in the phase diagram has been extensively studied in alloys binary uids and polymer mixtures 1 Alloys and binary uids can be reasonably explained by conventional theories of CahnHillard 2 or the HohenbergHalperin notation 3 where the interfacial tension plays a major role in deter mining the morphology For thermally quenched polymer mixtures Takana has shown that dynamic asymmetry can result from the slow kinetics associated with the polymer glass transition and that in this case the domain shape is determined by the mechanical balance of elastic forces resulting in spongelike continuous patterns of the minority polymer phase to form 4 For reactioninduced phase separation in binary polymer mixtures TranCong and Harada have demonstrated that a variety of mesoscopic structures can form with elastic stress playing an important role in the morphology when the reacting polymer is a minority phase 5 An interesting variant of this problem has been to understand phase separation kinetics when the polymer is diluted in an anisotropic solvent such as liquid crystals Here one has three competing dynamics one dominated by the transition from isotropic to nematic ordering of the liquid crystal a second determined by the phase separation of the polymer from the liquid crystal solvent where the anisotropy of the solvent can affect solubility and a third determined by the growing molecular weight and gelation of the polymer matrix 6 Recently Boots et al have shown that elastic forces in the polymer matrix also play a role in determining the morphology in polymer dispersed liquid crystal PDLC systems 7 In t is Letter we use time resolved confocal microscopy at high resolution 200 nm and high speed 100 ms to study the reactioninduced phase transition kinetics in polymermonomer liquid crystal mixtures very near the initial phase separation We observe unusual hydrodynam ics and coalescence which are not explained by current the ories of reactioninduced phase separation but dramatically affect the nal morphology We determine the kinetic phase separation diagram for a spongelike polymer liquid crystal composite and demonstrate that this phase dia 3276 0031 9007988015327641500 S0031900798058591 gram can be extended to other systems allowing us to predict the temperature and composition dependence of the nal morphology in dropletlike PDLC systems also Finally we observe a crossover from elastic to the hy percoalescence dominated regimes via the dilution of the monomer polymer The monomer used in this work Merck PN393 2ethyl hexyl acrylate monomer and trimethylol propane tria acylate crosslinker and the liquid crystal Merck TL2l3 halogenated biphenyl were chosen because they have been well studied and are known to form a spongelike morphology at low monomer concentrations upon irradia tion The critical concentration range for spongelike mor phology is 27 to 18 monomer by volume 89 The dynamics are similar over this range39 we concentrated our studies on 20 monomer solutions For comparison we also studied a mixture of the monomer Norland Optical Adhesive 65 NOA65itrimethylolpropane diallyl ether trimethylolpropane tristhiol and isophorone diisocyanate ester and the liquid crystal Merck E7 cyanobiphenyl compounds which results in a droplet morphology over a large composition range of monomer from 20 to 60 10 The mixture of monomer and nematic liquid crys tals results in an isotropic solution at room temperature prior to photopolymerization A uorescent dichroic dye Exciton pyrromethane 580 was used to increase con trast between the polymer and the liquid crystal The temperature range was bounded by the isotropicnematic transition near 15 C and the lack of a visible phase sepa ration on full polymerization near 70 C The phase di agrams for the PN393TL2l3 and NOA65E7 mixtures have been reported elsewhere 810 We used both 10 and 25 rm gap cells to show that the phase separation dynamics does not depend on surface interactions with the cells prepared as described previously 9 A Nikon2 Optiphot microscope Technical lnstrument s confocal at tachment and a 14 NA 100gtlt oilemersion lens yielded an effective resolution of 200 nm horizontal and 400 nm vertical The Hg lamp on the microscope with an esti mated power output of 10 mWcm2 at 365 nm was used to initiate the free radical polymerization over a limited area 200 rm X 200 Mm this unique geometry allowed 1998 The American Physical Society VOLUME 80 NUMBER 15 PHYSICAL REVIEW LETTERS 13 APRIL 1998 us to take several measurements on the same cell poly merize uniformly relieve contractioninduced stress 5 and take data simultaneous with the polymerization 11 The phase separation movie consisted of over 40 digi tal images which were taken with a 12bit Xillex Mirco imager camera In Fig 1 we show the time resolved morphologies of the PN393TL213 polymer liquid crystal mixture at 20 polymer concentration and at low 21 C and high 38 C temperatures where the frames are limited to six each for space considerations In frame 1 we rst observe the nucleation of the nematic liquid crystal domains caused by the increase in the liquid crystalline molecule nearest neighbors as the monomers react to form polymers As the addition polymerization reaction continues nematic domains continue to nucleate but are mainly static ie they do not move or grow in size via Oswald ripening or molecular diffusion until fast movement followed by very rapid coalescence starts to be observed in frame 3 To our knowledge coalescence of this nature has not been previously observed in PDLCs this could be due to the small size scale and short time scale for which these dynamics exist The fast kinetics occurs for a few seconds after which the hypercoalescence ceases because the polymer matrix has either grown suf ciently in molecular weight or reached its gel point impeding further coalescence Next the polymer and remaining solution continue to expel liquid crystal causing the nematic domains to grow in radius for several seconds until visible changes in the matrix are suppressed and longerterm elastic effects are expected to dominate The resulting morphology consists of liquid crystal domains dispersed in a spongelike polymer matrix with the domain size increasing with increasing UV cure temperature These dynamics are unique to the polymerization induced phase separation thermally quenching the sample below its diluted isotropicnematic phase transition T 15 C results in domain growth primarily by nucleation and growth Oswald ripening and molecular diffusion in agreement with standard theories of phase separation in binary uids 1 Free radical polymerization at high temperatures T 70 C above the pure liquid crystal isotropicnematic transition results in zero effec tive cross linking subsequent heating and cooling through this transition causes the polymer matrix to undergo a swellingdeswelling transition with no hypercoalescence and subsequent minor changes in nal morphology These results are consistent with the polymer acting as a microgel 12 We summarize our results using three time scales tn the time its takes for the nematic domains to grow to an observable size representative of the LC isotropicnematic phase transition tc the time when the hypercoalescence is initiated and tg the time for the polymer matrix to suf ciently solidify or gel such that elastic effects dominate The temperature dependence if tn circles tc squares and tg triangles at 15 lt T lt 45 C is summarized in 20 PN393I21C 20 PN393 43C FIG 1 20 PN393 monomer mixed with liquid crystal TL213 polymerized at 21 C left side and 38 C right side showing the rapid coalescence and hydrodynamics Above 40 and 60 sec respectively coalescence in no longer observed Images are 138 X 138 um Fig 2 for the TL213PN393 system The transition time for the isotropicnematic transition tn increases with increasing temperature as the distance from the phase boundary line increases 8 The fast kinetics and hyper coalescence time tc are temperature independent This 3277 VOLUME 80 NUMBER 15 PHYSICAL REVIEW LETTERS 13 APRIL 1998 5quotquotquotquotlquotquotquotquotquotII Elasticity tn tg Isotropic 45 Elasticity 4 Time seconds U I r N I C P 2 H O P O quotU 2 O I Isotropic 1 I I I 20 25 30 35 40 45 Temperature C FIG 2 Time after free radical initiation versus cure tempera ture diagram for PN393TL213 mixture main and NOA65E7 mixture inset The different regimes are explained in text Lines are guides to the eye result combined with studies at different polymerization rates indicate that tc depends on the extent of polymer ization and not on the fraction of nematic liquid crystal that has phase separated which is strongly temperature dependent Finally we observe that the solidi cation or gel time increases with increasing temperature as does the difference tg tc allowing for longer hypercoalescence times and therefore explaining the larger nal domains observed The increase in the solidi cation time is due to the increase in the solubility of the LC in the monomer as temperature increases 12 Phase separations explained by the usual thermody namic arguments based on the extent of the polymer ma trix at the isotropicnematic phase transition would expect smaller domains at higher temperature as is found for the wellstudied E7NOA65 system 6710 For compari son we repeated these experiments on the E7 NOA65 sys tem which allowed us to achieve monomer concentrations as high as 60 by volume At room temperature the E7 liquid crystal phase separated om the NOA65 monomer at 20 monomer concentration therefore the cell was heated to 35 C in order to get a homogeneous solution at 20 for direct comparison to the TL213PN393 systems We observe the same dynamics and phase diagram as be fore with the E7 forming a more dropletlike morphol ogy These dynamics are shown on the left side of Fig 3 If the monomer concentration is increased to 40 then these dynamics cease to occur right side of Fig 3 and we recover the results and morphology observed previously 7 The phase diagram for the 40 E7NOA65 system is shown in the inset of Fig 2 it is qualitatively the same as in the main gure but with a lowering of tg with respect to tn which results in the solidi cation point occurring before the nucleation of the nematic domains tg lt tn tg is effectively lowered due to the increase in mono mer concentration 12 For tg lt tn elastic effects domi 3278 20 Noquot FIG 3 Mixtures of liquid crystal E7 with 20 NOA65 monomer polymerized at 35 C left side and 40 NOA65 monomer polymerized at 21 C right side The rapid coales cence is observed only for low monomer concentrations Im ages are 138 X 138 um nate as recently shown by the Phillips group 7 and no hypercoalescence is observed In all systems studied the initial nucleation regime tc gt t gt tn is characterized by a quasiperiodic spatial appearance of nematic domains and the lack of any signi cant movement or growth of domains


Buy Material

Are you sure you want to buy this material for

25 Karma

Buy Material

BOOM! Enjoy Your Free Notes!

We've added these Notes to your profile, click here to view them now.


You're already Subscribed!

Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'

Why people love StudySoup

Bentley McCaw University of Florida

"I was shooting for a perfect 4.0 GPA this semester. Having StudySoup as a study aid was critical to helping me achieve my goal...and I nailed it!"

Anthony Lee UC Santa Barbara

"I bought an awesome study guide, which helped me get an A in my Math 34B class this quarter!"

Steve Martinelli UC Los Angeles

"There's no way I would have passed my Organic Chemistry class this semester without the notes and study guides I got from StudySoup."


"Their 'Elite Notetakers' are making over $1,200/month in sales by creating high quality content that helps their classmates in a time of need."

Become an Elite Notetaker and start selling your notes online!

Refund Policy


All subscriptions to StudySoup are paid in full at the time of subscribing. To change your credit card information or to cancel your subscription, go to "Edit Settings". All credit card information will be available there. If you should decide to cancel your subscription, it will continue to be valid until the next payment period, as all payments for the current period were made in advance. For special circumstances, please email


StudySoup has more than 1 million course-specific study resources to help students study smarter. If you’re having trouble finding what you’re looking for, our customer support team can help you find what you need! Feel free to contact them here:

Recurring Subscriptions: If you have canceled your recurring subscription on the day of renewal and have not downloaded any documents, you may request a refund by submitting an email to

Satisfaction Guarantee: If you’re not satisfied with your subscription, you can contact us for further help. Contact must be made within 3 business days of your subscription purchase and your refund request will be subject for review.

Please Note: Refunds can never be provided more than 30 days after the initial purchase date regardless of your activity on the site.