Supporting Information
Structures of Poly(3-hexylthiophene) Films Prepared from Binary Solvent Mixtures
Lawson T. Lloyd, Madeleine P. Gordon, David S. Boucher
Department of Chemistry and Biochemistry, School of Sciences and Mathematics, College of Charleston, Charleston,
South Carolina 29424
Supplementary UV/Vis Absorbance Spectra
FIGURE S1 Normalized UV/Vis absorbance spectra of (a) low molecular weight (L-Mw) and (b) high molecular
weight (H-Mw) P3HT in the 40:60 CF:HEX solvent mixture. Each panel shows the spectrum for aged 0.1 mg·mL–
1
, and 0.3 mg·mL–1 dispersions.
1
FIGURE S2 Normalized UV/Vis absorbance spectra of (a) low molecular weight (L-Mw) and (b) high molecular
weight (H-Mw) P3HT in the 30:70 CF:AcN solvent mixture. Each panel shows the spectrum for aged 0.1 mg·mL –
1
, and 0.3 mg·mL–1 dispersions.
2
Extracting the Aggregate Spectrum
FIGURE S3 Method used to extract the aggregate absorbance spectrum (–––) by removing the scaled amorphous
contribution from (---) from the raw absorbance spectrum (–––). The procedure is taken from ref. 1.
Determining the Extent of Aggregation1
This method assumes that there are only two species in the dispersion: a residual, non-aggregated amorphous phase
and the P3HT aggregates. The absorbance of the residual amorphous P3HT phase is approximated by scaling the
raw amorphous spectrum (recorded at the same concentration as the dispersion, e.g., 0.1 mg·mL–1) to the high
energy edge of the dispersion spectrum (Figure SX). As shown in Figure SX, the aggregate absorbance spectrum is
extracted by removing the scaled amorphous spectrum from the spectrum of the P3HT dispersion. The area under
the aggregate spectrum, , ΔAaggregate, (the cross-hatched region in Figure SXX) is a measure of the oscillator strength
of the P3HT aggregates. Similarly, the difference between the raw and scaled amorphous P3HT spectra, ΔAamorphous,
(the gray area in Figure SXX) reflects the change in the amorphous phase oscillator strength. The relative oscillator
strength, F, of the amorphous and aggregate phases in the dispersion is given by the ratio,
𝐹 =–
∆𝐴𝐴𝑔𝑔𝑟𝑒𝑔𝑎𝑡𝑒
∆𝐴𝐴𝑚𝑜𝑟𝑝ℎ𝑜𝑢𝑠
which, in turn, is related to the molar extinction coefficients (),
𝐹=
𝐴𝑔𝑔𝑟𝑒𝑔𝑎𝑡𝑒
𝐴𝑚𝑜𝑟𝑝ℎ𝑜𝑢𝑠
Because all of the P3HT chains removed from the amorphous phase are incorporated into the aggregate phase, once
the relative oscillator strength is calculated the fraction of aggregated P3HT is obtained from the absorbance spectra
of the amorphous and aggregate phases.
3
FIGURE S4 Method used to estimate the extent of aggregation of P3HT. The area under the aggregate
absorbance curve, ΔAaggregate, (cross-hatched) and the difference between the raw and scaled amorphous P3HT
spectra, ΔAamorphous, (gray area) are a measure of the relative oscillator strengths of the amorphous and aggregate
components.
TABLE S1 Relative Oscillator Strength, F,and Fraction of Aggregates
P3HT
F
%Agg
20:80 (v%:v%) CF:DCM
L-Mw
1.50
42
H-Mw 1.50
57
40:60 (v%:v%) CF:HEX
L-Mw
1.53
46
H-Mw 1.60
58
30:70 (v%:v%) CF:AcN
L-Mw
1.36
58
H-Mw 1.49
60
4
Dynamic Light Scattering
FIGURE S5 DLS particle size distributions of amorphous H-Mw and L-Mw P3HT in chloroform.
5
Thermodynamic Equilibrium and the Impact of Solution Preparation
The methods used to prepare P3HT dispersions affects their properties, e.g., excitonic coupling values and
extent of aggregation.2 To assess the impact of different preparation techniques on the assemblies in our
solvent mixtures, we prepared L-Mw and H-Mw samples in CF:HEX and CF:DCM by sonicating 0.1 mg·mL–
1
dispersions for 4 minutes prior to aging for 24 hours. We chose to use sonication because several groups
have shown that this method improves the yield and structural order of assembled P3HT nanofibers in
pure solvents.3-5 To our knowledge the effect of sonication on P3HT assembly in solvent mixtures has not
been investigated. In addition to sonication, we prepared a 0.1 mg·mL–1 dispersion of L-Mw P3HT in 20:80
CF:DCM by adding the DCM slowly over a 24 hour period via an automated syringe pump. We measured
the UV/Vis spectra after 24 hours and then again 1 week later. The excitonic coupling values are given in
Table S2.
TABLE S2 Excitonic Coupling Values Using Different Dispersion Preparation Methods
J (L-Mw) J (H-Mw)
[meV]
[meV]
20:80 (v%:v%) CF:DCM
Aged (24 hr)
11
11
Aged (1 week)
11
11
Slow DCM Add (24 hr)
6
--Slow DCM Add (1 week)
8
--Sonicated (24 hr)
9
8
Sonicated (1 week)
9
8
40:60 (v%:v%) CF:HEX
Aged (24 hr)
10
10
Aged (1 week)
11
11
Sonicated (24 hr)
11
12
Sonicated (1 week)
12
13
System
After 24 hours the excitonic coupling values of the sonicated dispersions in CF:HEX are slightly larger than
the non-sonicated sample. The increase for L-Mw P3HT is on the edge of  1 meV error bar. However, for
these studies we are using aliquots of the same solution aged for 1 week, i.e., with no further dilution, so
we believe that a 1 meV change is significant. After one week of aging the J values of the non-sonicated
and sonicated dispersions increase by 1 meV, which contrasts with the behavior of the CF:DCM
dispersions. In CF:DCM the excitonic coupling values of the sonicated dispersions are slightly smaller than
those prepared without sonication. For both of these methods the J values are do change by 1 meV after
one week of aging. The dispersion prepared by slow addition of DCM exhibits a 6 meV J value after 24
hours, and this value increases to 8 meV after one week of aging. These excitonic coupling values are
significantly lower than the 11 meV values obtained for solutions prepared by rapid addition of DCM and,
as show in Figure S6, the lower J values can be rationalized based on the large amount of amorphous P3HT
left in these solution. Our analysis estimates that the extent of aggregation is 20% and 30% in these
dispersions and as the amorphous phase decreases, the J values increase, which is consistent with chain
fractionation arguments. It is notable that the slow addition of the DCM solvent gives rise to a larger
change in the extent of aggregation over an additional one week aging period. Based on these
observations and results of our previous work,6 solvent mixtures containing DCM may prove extremely
useful to monitor the real-time assembly and crystallization of P3HT in the liquid phase.
6
FIGURE S6 UV/Vis absorbance spectra of low molecular weight (L-Mw) P3HT dispersions (0.1 mg·mL–1) in a 20:80
CF:DCM solvent mixture. The spectra are normalized to an approximate isosbestic point at 510 nm. The solid (—)
spectrum shows the absorbance of dispersions made following the slow addition of DCM over a period of 24 hours.
The dotted (·····) spectrum is the same dispersion that was left to age for 1 week. The dashed spectrum (----) is
corresponds to a dispersion prepared by rapid addition of DCM and a 24 hour aging time, i.e., the same as in Figure
1(a).
Confocal Microscopy
FIGURE S7 Optical micrograph of H-Mw P3HT films cast from the same 0.1 mg·mL–1 dispersion and dried under (a)
slow and (b) rapid evaporation conditions. The images were taken using a 10× (NA = 0.3) objective. The tapping
mode AFM image (25 μm × 25 μm) of (b) is shown in Figure S8.
7
Additional Atomic Force Microscopy Images
FIGURE S8 Tapping mode AFM image (25 μm × 25 μm) of H-Mw P3HT drop cast from pure chloroform and dried under
rapid evaporation conditions.
FIGURE S9 Tapping mode AFM image of L-Mw P3HT drop cast from 30:70 CF:AcN and dried under slow evaporation
conditions that shows the extent and density of the dot-like structures across a larger (20 μm×20 μm) region.
Honeycomb Pattern of Films Cast from 20:80 CF:DCM
Marangoni Effects
Marangoni instabilities arise due to surface tension and/or viscosity gradients in the evaporating polymer
solution. The viscosity (η) and surface tension (σ) of chloroform (σ = 27.2 dyne·cm–1, η = 0.57 cP) and
dichloromethane (σ = 28.2 dyne·cm–1, η = 0.44 cP) are not significantly different;7 thus, it is unlikely that
Marangoni effects related solely to “static” differences between η and σ of the solvents are the dominant
mechanism of honeycomb formation in the P3HT films.8 However, we propose that several other factors
may promote Marangoni effects: (1) the addition of water due to evaporative cooling, (2) the changing CF
and DCM compositions during the lateral drying process, and (3) the different solubility of P3HT in CF,
DCM, and water, which are good, marginal, and poor solvents for P3HT. The first point may help account
for the time-dependent growth of the pore size, as shown in Figure 6 (main text). Both CF and DCM have
a low solubility in water (XCF  0.0012 and XDCM  5×10–4). In fact, chloroform and water are a well-known
heteroazetrope. Thus, as water droplets condense on the surface it is reasonable to assume that liquidliquid demixing occurs between water and the CF:DCM blend. In this case, the time dependent pore
8
growth is a result of parallel water droplet nucleation and growth and the changing liquid composition
due to rapid evaporation of DCM. The insolubility of P3HT in water causes the colloidal P3HT particles and
amorphous P3HT to move into the CF:DCM phase, thereby establishing a P3HT-rich CF:DCM phase and a
P3HT-lean aqueous phase. The partitioning of P3HT coupled with the changing composition of the
CF:DCM blend and the growth of the aqueous domains may give to rheological and surface tension
variations that promote (solutal) Marangoni effects between P3HT-rich and P3HT-lean phases.
Convective Assembly
Convective assembly was first observed by Perrin in 1909 during his seminal work on Avogadro’s
number,9,10 but the details of this process weren’t clarified until 1992 when Denkov and co-workers
investigated the 2D crystallization of latex spheres.10-12 This process involves the assembly or
crystallization of colloid particles in evaporating films on solid surfaces by a two-step mechanism.13 A
cartoon of the process, as reported by Kralchevsky et al. (Figure 4 in ref. 12), is shown in Figure S10.12 In
the first step a hydrodynamic force, Fd, caused by a hydrodynamic flux, Jw, drags the particles in the thicker
solvent layers inward towards the thinner regions. The flux, Jw, compensates for the solvent evaporating
in the thinner region. The second step is crystal growth through convective particle flux, wherein the
colloid particles assemble via capillary immersion forces, F, in the thinner solvent region. In the second
step, the particle flux, and subsequent crystallization, is caused by the evaporation of the solvent from
the already ordered array.12
FIGURE S10 Cartoon showing the process of convective assembly. (a) A hydrodynamic force, Fd, caused by a
hydrodynamic flux, Jw, drags the colloidal P3HT particles in the thicker solvent layers inward towards the thinner
regions. The flux, Jw, compensates for the solvent evaporating in the thinner region. Crystal growth occurs through
convective particle flux, wherein the colloid particles assemble via capillary immersion forces, F, in the thinner
solvent region. The particle flux, and subsequent crystallization and patterning (b), is caused by the evaporation of
the solvent from the already ordered array. Adapted from ref. 12.
9
Solubility Parameter Differences, : Polymer/Solvent/Non-solvent Systems
The characteristics of asymmetric polymer membranes produced by phase inversion processes in
polymer/solvent/nonsolvent (p/s/ns) systems have been rationalized using criteria based on ternary
phase diagrams, Flory-Huggins parameters, solvent/non-solvent diffusion models, and Hansen solubility
parameter differences, to name a few.14-18 Although asymmetric membranes are processed using
techniques that are quite different from our simple drop casting methods,16 it is interesting to draw from
the extensive literature to address the morphological variations of our films. Of particular interest to us
are the kinetics and thermodynamics of liquid-liquid demixing and the precipitation and crystallization of
P3HT in the polymer-rich (good solvent) and polymer-lean (poor solvent) phases. Here, we use a factor,
, to correlate the morphology of our P3HT films to the nature of the polymer-solvent and solventsolvent interactions.
The  factor for a p/n/ns systems is obtained from the equation,17

Δδ p – s Δδ p –ns
δp Δδ s –ns
[2]
where the magnitude of the solubility parameter differences, Δδi–j, is a measure of the affinity between
the ith and jth component. We calculated the solubility parameters of the chloroform solvent (δ s), the
three non-solvent (δns), and the P3HT polymer (δp) using the Hansen parameter values available in the
literature. A detailed description of this process is given in the Supporting Information. Our results are
shown in Table 2
TABLE 2. Solubility parameters differences and  values
Δδp-s
Δδs-ns
Δδp-ns

[MPa1/2] [MPa1/2] [MPa1/2]
CF:DCM
4.83
3.29
6.06
0.488
CF:HEX
4.83
7.08
4.50
0.169
CF:AcN
4.83
15.13
15.90
0.279
Solvent
Ruann et al. developed , which they related to the miscibility gap and the size of two-phase region of
p/s/ns phase diagrams, as an accessible way to validate and predict the structure of asymmetric
membranes using solubility parameter differences.17 Several reports show that as the value of 
decreases the asymmetric membrane favor macrovoid, sponge-like, and bead-like structures, i.e.,
macrovoid > sponge > bead.17-19 Since we do not yet have phase diagrams for the p/s/ns systems used in this
study, we thought it would be worthwhile to test the correlation between  and the morphologies of our
films. Since this  is based on solubility parameters, which correlate with fundamental polymer solution
thermodynamics, e.g., Flory-Huggins theory,20-27 we confine our analysis to films dried under slow
evaporation conditions.
It is notable that the CF:DCM blend gives the largest  value, thereby suggesting a correspondence
between macrovoid structures in asymmetric polymer membranes and the honeycomb pattern of the
CF:DCM film. The spherical structures in CF:AcN and CF:HEX may parallel the bead structures, but without
an intermediate spongelike morphology we cannot verify this correlation. Frommer and Messalem
studied the formation of large macrovoids in membranes produced by phase inversion processes in
polymer/solvent/nonsolvent (p/s/ns) systems.28 They attributed these macrovoids to the initiation and
10
formation of convective flows near interfaces brought about by surface tension gradients. Solubility
differences of P3HT in chloroform and dichloromethane may produce localized rheological and surface
tension variations (Marangoni effects) due to mass transfer between P3HT-rich and P3HT-lean regions
during the drying process. This picture is consistent with the mechanism posited by Frommer and
Messalem.
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