Supporting Information
German Edition:
Silica-Based Liquid Marbles as Microreactors for the Silver Mirror
Reaction**
Yifeng Sheng, Guanqing Sun, Jie Wu, Guanghui Ma,* and To Ngai*
anie_201500010_sm_miscellaneous_information.pdf
DOI:
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Experimental Details
Materials: HDK® H30 and H18 silica particles were a gift from Wacker Chemie AG; 10 μm and 4.4
μm silica particles were from Suzhou Nanomicro Technology Company; silver nitrate (AgNO3,
99.80%) was purchased from UNI-Chem; magnesium chloride hexahydrate (MgCl2∙6H2O, 99.00%),
and delta-gluconolactone (C6H10O6, 99%) were purchased from Acros; ammonia solution (NH3∙H2O,
25%) was purchased from BDH Chemicals; D(+)-glucose (C6H12O6, AR) was purchased from
Normapur; toluene (C7H8, 99.70%) was purchased from Sigma-Aldrich; microscope slide was from
Fisher Finest. All chemicals were used without further purification. Deionized water was used to
prepare all the solutions.
Preparation of [Ag(NH3)2]OH aqueous solution: 1.5 g AgNO3 was dissolved in 8.5 g deionized
water, and then 5 wt% ammonia solution was added under vigorous magnetic stirring until a clear
colorless solution was obtained. The newly formed diamminesilver(I) solution was finally diluted to
different concentration by adding deionized water.
Preparation of glucose solution: 1 g C6H12O6 was dissolved in 9 g deionized water first. By adding
deionized water, ethanol or Tween 80, different glucose solutions with different concentrations could be
prepared.
Preparation of particle blends: particle blends were prepared according to mass ratio. For example,
H30:H18=3:1 blend was prepared by mixing 0.15 g H30 particles with 0.05 g H18 particles.
Surface modification of 10 μm silica particles: 0.5 g silica particles were first dispersed to 50 mL
toluene, and then 0.5 g dichlorodimethylsilane were added. After 24 hours reaction under dry N2,
particles were separated from toluene by centrifugation, and then washed by methanol and ethanol, and
finally freeze-dried under vacuum.
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The silver mirror reaction is listed below.
Preparation of liquid marbles
Typically, 15 μL glucose (or gluconolactone) solution was first placed on a bed of silica particles, then
15 μL diamminesilver(I) solution was injected into the droplets, after rolling, normal liquid marbles
were prepared.
Liquid marbles with different coverage: 15 μL 5.0 wt% glucose solution was first placed on a bed of
H30 particles (or hydrophobic glass) first, then 15 μL 5.0 wt% diamminesilver(I) solution was injected
into the droplets, by moving the silica particles instead of rolling the droplets, marbles with different
coverage were prepared (Figure S1).
Janus liquid marbles: in the first stage, H30- and H18-coated marbles were prepared on an A4 paper;
then the paper was rolled up to merge the liquid marbles, and the Janus liquid marbles were prepared
(Figure S2). The kinds and the volume of solution used in this part were as follows: (a) 75 μL
diamminesilver solution (H18) and 25 μL glucose solution (H30); (b) 60 μL diamminesilver solution
(H18) and 30 μL glucose solution (H30); (c) 50 μL diamminesilver solution (H18) and 50 μL glucose
solution (H30); (d) 60 μL diamminesilver solution (H30) and 30 μL glucose solution (H18); (e) 75 μL
diamminesilver solution (H30) and 25 μL glucose solution (H18).
Liquid marbles containing ethanol or Tween 80: 15 μL 1.0 wt% diamminesilver(I) solution was first
placed on a bed of silica particles first, then 15 μL 1.0 wt% glucose ethanol/aqueous solution or 15 μL
1.0 wt% glucose/Tween 80 was injected into the droplets. After rolling, normal liquid marbles were
prepared.
 All the concentrations in the manuscript and the Supporting Information are the initial
concentrations of the solutions before mixing.
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Calculation of the Ag shell thickness formed by the silver mirror reaction:
Basis: one liquid marble containing 15 μL 5.0 wt% glucose solution and 15 μL 5.0 wt%
diamminesilver(I) solution (the solute is Ag(NH3)2OH).
The total mass of Ag:
mAg = 30 × 10-3 g × 2.5% × 67.87 % = 5.1 × 10-4 g
Density of Ag is 10.49 g/cm3
The volume of Ag formed by the silver mirror reaction:
VAg = 4.9 × 10-5 cm3
Assuming that the liquid marble is spherical, thus
4/3 × π × rmarble3 = 30 × 10-3 cm3
rmarble = 0.193 cm
The surface area of the liquid marble:
S = 4π × rmarble2 = 0.467 cm2
The thickness of the silver film:
d = 1.0 × 10-4 cm = 1.0 μm
Figure S1. Preparation of liquid marbles with different coverages.
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Figure S2. Preparation of Janus liquid marbles: a) H30- and H18-coated marbles are prepared; b)
merging the marbles gives rise to the Janus marble; c) due to different surface properties, silver mirror
reaction preferentially occurs on H30 particles.
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Figure S3. Photo images of “liquid marbles” at 1 minute and 60 minute after preparation: (A) a mixed
uncoated solution droplet on a glass substrate; (B) an only bottom-coated liquid marble; (C) a topopened liquid marble; (D) a fully-coated liquid marble. Scale bar: 1 mm.
Figure S4. Photo images of liquid marbles with varied diamminesilver(I) and glucose concentrations
captured at different reaction stages: (A) liquid marbles with fixed diamminesilver(I) concentration and
increasing glucose concentrations. From a to g: 0, 0.1 wt%, 0.5 wt%, 1 wt%, 3 wt%, 5 wt% and 7 wt%;
(B) liquid marbles with fixed glucose concentration and increasing diamminesilver(I) concentrations.
From a to g: 0, 0.1 wt%, 0.5 wt%, 1 wt%, 3 wt%, 5 wt% and 7 wt%. Scale bar: 1 mm.
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Figure S5. SEM images of different silica particles: (A) H30 particles; (B) H18 particles. Scale bar: 100
nm.
Table S1. Parameter of silica particles
H30 particles
H18 particles
SiO2-content (%)
>99.8
Density of SiO2 (g/L)
2200
Silanol group density (SiOH/nm2)
1
Electric resistivity (density 40 g/l) (Ω∙cm)
BET-surface area (m2/g)
BET-surface area of hydrophilic silica (m2/g)
Carbon content (%)
pH, in 4 % dispersion
Surface modification
<0.5
>1013
ca. 250
ca. 120
270 - 330
170 - 230
ca. 1.8
ca. 4.5
3.8 – 4.5
4.0 – 6.8
-OSi(CH3)2-
Figure S6. Static contact angles of liquid marbles fabricated using pure water with different particles.
From left to right, the volumes were 5, 10, 20, 30, 50 μL. Scale bar: 1 mm.
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Table S2. The parameters of liquid marbles with different volume
H30 particle
Size (μL)
5
10
20
30
50
d (mm)
2.2
2.8
3.6
4.2
5.1
h (mm)
1.8
2.3
2.9
3.2
3.6
l (mm)
1.3
1.7
2.3
2.9
3.6
Size (μL)
5
10
20
30
50
d (mm)
2.1
2.7
3.5
4.2
5.1
h (mm)
1.7
2.2
2.7
3.0
3.4
l (mm)
1.3
1.8
2.4
3.2
3.8
H18 particle
Figure S7. Color changes of one Janus droplet (VH30:VH18=1:1): from left to right, the reaction time was
1, 3, 5, 10, 15 minute, successively. Scale bar: 1 mm.
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Figure S8. Plan view of different liquid marbles during evaporation: (a) pure water; (b) gluconolactone
and diamminesilver(I); (c) glucose and diamminesilver(I).