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Supporting Information

Fabrication of Liquid Protrusions on Non-

crosslinked Colloidal Particles for Shape-

controlled Patchy Microparticles

Lei Tian, Xue Li, Panpan Zhao, Zafar Ali and Qiuyu Zhang*

Department of Applied Chemistry, School of Science, Northwestern Polytechnical

University, Xi’an 710072, China

The Key Laboratory of Space Applied Physics and Chemistry, Ministry of Education,

Northwestern Polytechnical University, Xi’an 710072, China

*Corresponding author:

E-mail: qyzhang@nwpu.edu.cn.

Tel: +86-029-88431675;

Fax: +86-029-88431653.

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Figure S1. (a) SEM image of non-crosslinked PGMA particles prepared by dispersion

polymerization. (b) DLS size distribution of PGMA particles.

a

b

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Figure S2. Asymmetric monomer-swollen particles prepared by swelling PGMA seed

particles used GMA as swelling monomer. The red broken circles and green circles

marked the dimer-like MSPs and snowman-like MSPs, respectively.

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a b c d e

1.5

3.0

4.5

6.0

7.5

Dia

mete

r (μ

m)

Sample

Figure S3. Average particle size of PGMA/PS patchy microparticles prepared with

various weight ratio of DBP/St. (a) PGMA seed particles, (b) 1.0/2.5, (c) 2.5/1.0, (d)

2.5/2.5, (e) 5.0/5.0.

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Figure S4. Average particle size and DLS size distribution of PGMA/PS patchy

microparticles prepared with different content of Sp.

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Figure S5. SEM images and optical microscope photographs of microparticles after

swelling and polymerization. The seed particles were PS (a, b), PMMA (a’, b’).

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40 60 80 100 120 140

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

Heat F

low

(m

W)

Temperature (°C)

PGMA

PS

PMMA

70°C

98°C

126°C

Figure S6. DSC traces of pure PGMA, PS and PMMA seed particles prepared by

dispersion polymerization.

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The formation mechanism of PGMA/PS patchy microparticles

The DBP/St ratios have a great influence on the monomer-swollen seed particles in

Figure 2. To further investigate the effect of the polymeric monomer (Sp) added in the

polymerization stage, PGMA/PS microparticles prepared with no Sp were shown in

Figure S7. The prepared microparticles exhibit bowl-shaped structure, rather than

patchy morphology as shown in Figure 4d. The result indicates that Sp similarly plays

an important role in the morphology control of patchy microparticles.

Figure S7. SEM images of swollen PGMA seed particles (a) and polymeric PGMA/PS

microparticles (b) prepared with DBP/St weight ratio of 2.5/2.5. The initiator was

dissolved in swollen monomer, and no Sp was added.

Then, in order to clarify the formation mechanism of PGMA/PS patchy

microparticles, the polymerization process was tracked as shown in Figure S8 and S9.

Before the polymerization of 1 h, the formed microparticles keep the single-hole

structure as the same as swollen PGMA seed particles which have been discussed in

Figure 1. As the polymerization performing, heterogeneous nucleation of St occurred

on the surface of swelling PGMA seed particles as shown in Figure S8 when the

polymerization time was 2-3.5 h. During this period, polymeric monomer was

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expended, and monomer conversion was increase rapidly (Figure S9g).

Figure S8. The SEM images of prepared PGMA/PS microparticles prepared at

different polymerization times. The DBP/S ratio was fixed at 2.5/2.5, and Sp was 1.0 g.

The determination of monomer conversion. Monomer conversion was determined as

follows: 1.5 g of PGMA seed particles was dispersed in 100 mL 0.25 wt% SDS aqueous

solution. Then, 7.58 g of swelling agent (DBP) and 7.53 g of styrene were added. After

swelling for 24 h, the mixture was poured into a three-necked flask, and added 3.03 g

of styrene dissolved with AIBN. Finally, the reaction system was heated to 80°C to

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initiate polymerization. At different time points, W1 g mixture was took out, and added

W2 g inhibitor hydroquinone, washed with methanol for 3 times by centrifugation, and

vacuum drying. Then, the dried mixture was weighted (W3). The corresponding

monomer conversion was calculated according to the formula as follows:

3 2 1

1

1.5 /100 % 100%

7.53 3.03 /100

W W WConversion

W

Subsequently, the above microparticles were further swollen by monomer. At this

moment, monomer conversion remained almost constant (4-6.5 h). When the

polymerization was proceeded for 6.5 h, many small protrusions were appeared on the

surface of these microparticles though the polymerization of swollen monomer. The

phase separation of the protrusions and PGMA seeds was more distinct. With the

growth of the protrusions, we obtained PGMA/PS patchy microparticles as shown in

Figure 4d.

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Figure S9. (a, a’) Schematic illustration of morphology evolution of PGMA/PS patchy

microparticles. (b-f, h-l) morphology evolution of PGMA/PS patchy microparticles

prepared at different polymerization times. (g) Monomer conversion of PGMA/PS

patchy microparticles.

According to the above mentioned analysis, we propose the formation mechanism of

PGMA/PS patchy microparticles as shown in Scheme S1. When the dosage of Sp was

low, the liquid protrusions on monomer-swollen PGMA particles served as monomer

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warehouses, supporting the polymerization in the presence of insufficient Sp. The

liquid protrusions were disappeared as the polymerization performing (Scheme S1a),

and single-hole patchy microparticles with small protrusions were formed (Figure 5a,

b). When the dosage of Sp was high, most liquid protrusions were solidified and

survived by the polymerization in the presence of sufficient Sp to form irregular patchy

microparticles (Scheme S1b). Then, these irregular patchy microparticles were further

swollen by additional monomer, and polymerized into PGMA/PS patchy microparticles

with small protrusions. Further, these protrusions regrew, and PGMA/PS patchy

microparticles with large protrusions were synthetized (Figure 5).

Scheme S1. The formation mechanism of PGMA/PS patchy microparticles.

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Figure S10. The patchy coefficient β of morphological evolution of PGMA/PS patchy

microparticles. β was defined to evaluate the effect of microparticles structure on the

reflectance, (a) was at 266 nm and (b) was at 1680 nm.

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Calculation of patchy coefficient β

Patchy coefficient β was defined and measured for the probability of light irradiated

on the patchy microparticles, and calculated as follows:

β =∑𝑆 ∑𝑉⁄

Where ∑𝑆 was the sum of the total surface area, ∑𝑉 was the sum of the total

volume.

(1) For PGMA seed particles. β was obtained by surface area and volume of the sphere

as shown in Figure a.

β = 4𝜋𝑟02 4

3⁄ 𝜋𝑟03⁄

(2) For patchy microparticles prepared by 1.5/1.5 of DBP/S.

β = 4𝜋𝑟12𝑛 4

3⁄ 𝜋(𝑟2−𝑟1)3⁄ , n=16

Where n was the average number of protrusions.

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(3) For patchy microparticles prepared by 5.0/5.0 of DBP/S.

β = (4𝜋𝑟52𝑛 + 4𝜋𝑟3

2 − 𝑆′) (4 3⁄ 𝜋(𝑟3 + 𝑟4)3 − 𝑉′)⁄ , n=13

Where S’ and V’ were the surface area and volume of spherical cap which was the

intersecting part of circled geometries.

(4) For patchy microparticles prepared by 4.0 g of Sp.

β = (4𝜋𝑟72𝑛1 + 4𝜋𝑟8

2𝑛2) (4 3⁄ 𝜋(𝑟6 − 𝑟8)3)⁄ , 𝑛1 = 5, 𝑛2 = 8

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(5) For patchy microparticles prepared by 3.0 g of Sp.

β = (4𝜋𝑟92 + 4𝜋𝑟11

2𝑛3) (4 3⁄ 𝜋(𝑟93+(𝑟10− 𝑟11)3))⁄ , 𝑛3 = 30

(6) For patchy microparticles prepared by 2.5/2.5 of DBP/S.

β = (4𝜋𝑟122 + 4𝜋𝑟14

2𝑛4) (4 3⁄ 𝜋(𝑟123+(𝑟13− 𝑟14)3))⁄ , 𝑛4 = 30

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Figure S11. The process of hexadecane droplets sitting on the membrane assembled by

acid-treated patchy microparticles.

Figure S12. The picture (a) and the water contact angle (b) of the membrane assembled

by acid-treated PGMA.

Figure S13. The picture (a) and the water contact angle (b) of the membrane assembled

by acid-treated PS.

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Self-assembly mechanism of PGMA/PS patchy microparticle membranes

We have elucidated that high crosslinking density of particulate material prepared by

crosslinked seeds make it difficult to directly create functional membranes. Therefore,

it is necessary to find a procedure which can easily assemble PGMA/PS patchy

microparticles into functional membranes.

The epoxy ring of PGMA would hydrolyze which was catalyzed by acid to mainly

form a 1,2-diol product (product 1) [Sarah E. Shaw, Tiziana Russo, David H. Solomon,

et al. Polymer, 2006, 47, 8247-8252]. The reaction process is shown in the figure below

including: 1) water attacks the protonated carbonyl groups of PGMA. 2) The formed

hydroxyl groups attacks the protonated epoxy rings.

Figure S14. hydrolytic process of the epoxy ring of PGMA.

In this case, abundant hydroxyl groups will be created due to the hydrolysis of the

epoxy ring of our prepared PGMA/PS patchy microparticles treated by acid. We will

explain self-assembly mechanism of self-assembled particle membranes from the

following two points (Scheme S2):

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Scheme S2. Schematic diagram of self-assembly mechanism of PGMA/PS patchy

microparticle membranes.

(1) hydrogen bonding between the microparticles [C. Tapeinos, E. K. Efthimiadou,

N. Boukos, et al. J. Mater. Chem. B, 2013, 1, 194–203] by reason of the hydrolysis of

the epoxy rings of these patchy microparticles as illustrated in following figure,

enhances the interparticle interactions.

(2) When the hydroxyl groups attacks the protonated epoxy rings of another PGMA

polymer chains, it will form a cross-linking network as show in the figure below.

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Figure S15. The formation process of cross-linking network of PGMA.

The corresponding solid-state 13C NMR spectrum of hydrolysed PGMA particles has

been shown in our previous study [Chunmei Li, Jiaojun Tan, Hui Li, et al. Polym. Chem.,

2015, 6, 7100–7111]. In addition, we have measured crosslink density of acid-treated

PGMA/PS patchy microparticles by nuclear magnetic resonance crosslinking density

meter (NIUMAG, PQ001) as shown in Figure S16. By calculating, crosslink density of

acid-treated PGMA/PS patchy microparticles is 11.61 E-4 mol/cm3.

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0 200 400 600 800

1400

1600

1800

2000

2200

2400

2600

2800

3000

Se

map

ho

re

Relaxation time (ms)

Figure S16. Crosslink density of acid-treated PGMA/PS patchy microparticles

measured by nuclear magnetic resonance crosslinking density meter.

IR spectrum of acid-treated PGMA/PS patchy microparticles shows that the broad

peak at 3448 cm-1 is ascribed to the stretching vibration of O-H under the effect of

hydrogen bonding. The absorption peak of the epoxy group at 906 cm-1 is disappeared,

which indicates the hydrolysis of the epoxy rings. The glass transition temperatures (Tg)

of PGMA and PS are 70 and 98°C, respectively (Figure S6, Supporting Information).

In general, the Tg of copolymer of PS and PGMA will be 70~98°C. However, DSC

trace (Figure S18) shows that the Tg of acid-treated PGMA/PS patchy microparticles

is 143°C which is a considerably higher than PS and PGMA. The reason may be that

the existence of hydrogen bond and cross-linked network greatly enhance Tg of acid-

treated PGMA/PS patchy microparticles.

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4000 3600 3200 2800 2400 2000 1600 1200 800

0.5

0.6

0.7

0.8

0.9

1.0

Tra

nsm

itta

nce (

a.u

.)

Wave numbers (cm-1)

1128

3030 16953448

1026

Figure S17. IR spectrum of acid-treated PGMA/PS patchy microparticles.

40 80 120 160 200

-25

-20

-15

-10

-5

0

Heat F

low

(m

W)

Temperature (℃)

Figure S18. DSC trace of acid-treated PGMA/PS patchy microparticles.

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According to the above two kinds of interactions, these acid-treated PGMA/PS

patchy microparticles tend to assemble the membrane in Figure 8. In fact, when acid-

treated PGMA/PS patchy microparticles were washed with water/ethanol, these patchy

microparticles transform into a gel-like structure (“particle gel”) in Figure S19 and

Movie-S3.

Figure S19. The pictures of acid-treated PGMA/PS patchy microparticles with gel-like

structure in water/ethanol.

Movie-S1. Oil contact angle of acid-treated patchy material.

Movie-S2. Absorption of oil by acid-treated patchy material.

Movie-S3. Acid-treated PGMA/PS patchy microparticles with gel-like structure.